Most “disappeared” speakers.

No, you are not. You don’t come take my speakers away. Lol
Which speakers have craziest soundstaging and most disappeared image costing around $3-6k used or new, bookshelf or floorstanding.
(Need pointers, Not asking how to set them up 101.)
The most "full range" dynamic speaker that do the disappearing act would have to be Audio Physics, and then also most ESL’s and Planers.

Cheers George

Easy. MBL speakers.
I got my 121s for a steal years ago, but that was because they were damaged in shipping to someone else so they were sold cheap.
Nothing disappears/soundstages like the MBLs that I've heard.
Then again, it's rare to find them that cheap. 

Otherwise, I agree with george, Audio Physic speakers are reliable for a disappearing act (one of my other favorite brands). 
It's as much about the room and speaker placement than the speakers - maybe more.
You can try out Magnepan LRS with generous 60 days return policy.

Planar speakers are known for disappearing act.

I also pulled the trigger for LRS although I have nice dynamic speakers.
Charney Audio Companion Horns disappear with SS and tube gear. Soundstage is wide, high, and deep with superior tonal balance.

Whichever one I want.

That is not a flippant answer. If you know what you are doing any type of speaker can do this.

I do not recommend buying a set of speakers based on the perception that one will magically do this "disappearing" act better than another. If anyone is trying to sell you a speaker that way, run the opposite direction, because they are you or ignorant. :)

Buy the speaker based on your loving the overall characteristics of the sound. Setup and selection of components and cables will take care of the rest. 
BTW, that is not to say the soundstage characteristics of each will be the same. But, the effect of sensing the speakers have "disappeared" happens when they are setup properly. If you don't get that sense, then you likely have not set them up properly. YMMV 
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Coherency between drivers matters to avoid image shift of notes that span the crossover region.  Most speakers that get this right will disappear if placed properly with respect to the listening position.  The most impressive demonstration of this for me was with a pair of Harbeth M 40.2.  You could not detect a single note, artifact or sound localized to the speaker.  Every sound came from behind them as if on a 3-D virtual sound stage.  The key is to have lots of room behind the speakers, e.g. 5-6 feet if possible. 
i had a pair of crappy advent legacys get stolen from the garage rig.. those are so diasappeared i cannot hear them anymore
+1 to @douglas_schroeder  's posts.

Whichever one I want.

....the effect of sensing the speakers have "disappeared" happens when they are setup properly

Almost any speaker can be made to 'disappear' ... this is also about your system (not solely the speaker).
I haven't heard these in a while, but I have a soft spot for wide-baffle speakers. 

The Sonus Faber Stradivari are excellent examples. While small 2-ways often disappear if properly designed and out in the room, the wide baffle speakers have their own benefits and ease of integration, and are much more location friendly. Plus, I think they're gorgeous.
Vandersteen 2Ce Sig disappears about as well as any $peaker, even with the lights on and the signal in one channel.
Costco sells this thing you plug into the outlet. Then you plug your lamp into the thing. When you press the remote the light goes out. Speakers, everything, whole system disappears.
Hello nasaman,

     I agree with shkong78 that the new Magnepan LRS planar-dynamic panel speakers are an excellent choice.  These can definitely do the disappearing act but have a few requirements to do so; they need to be pulled out a minimum of about 3' from the wall behind them, need about 100 watts or more for optimum vanishing and are limited in bass response.
      Here's a youtube review:

     You have a healthy budget which results in many good options.  One excellent option would be to combine these $650/pr Magnepan panels with a $2,800 4-sub Audio Kinesis Swarm distributed bass array (dba) system for a total cost of $3,450 that I know would provide a very high quality, full-range and very unique version of a disappearing speaker system.  Here's a link to an Absolute Sound review of the Audio Kinesis Swarm dba system:

     However, your room would also need to have adequate space to accommodate 4  1'Wx1'Dx 2'H subs positioned around its perimeter.

     Another good option for disappearing speakers that's a bit simpler, and may better meet your needs,  would be a new or used pair of one of the current or former Magnepan speakers that are a bit larger and have more bass extension.  Good candidates would be the 1.6, 1.7i, 3.6, 3.7i, 20.1.  Remember,  all Magnepan speakers are dipoles, however, meaning sound is emitted from the front and back of the planar-magnetic panels and they all require at least a 3' space between the back of the panel and the wall behind.
     Could you state the size of your room and the amp you plan on using?

Ohm Sound Cylinders will embarrass all the touted, expensive box speakers! Expansive, room-filling 3-D sound. Beats Magneplanars! An astonishing speaker - I have a pair! Sadly not given any love from the snob-appeal crowd. Maybe if they came in a black-chrome finish and sold for $50K the high-rollers would covet them!
I agree with br3098 and Douglas Schroeder. Attention to details, such as proper room set up, and any speaker can do a disappearing act. 
+1 (again) to all those commenting on setup/placement.   
My current system with Lansche 4.1 also disappears although it is well beyond OP’s budget.

I agree with everybody that combination of front end, amplification, cables , room treatment and placement play in 3-D imaging or disappearing act.

But in general, planar speakers have advantage in wide and deep soundstage with disappearing act.

I recommend OP to try out Manepan LRS without any subwoofer whether it satisfy your need.

It may not rock but will be good for classical music or Jazz.

If you like LRS but if you want more dynamics or bass, then you can go for upper model or add subwoofer on it.

I also recommend OP to spend half of budget on digital front end or amplification.

Lyngdorf 2170 is very useful as DAC, D class int or pre amplifier and active crossover.

The new price starts from 4K$, but you can get used one around 3K$.

I wish you luck.

+1 prof. Mbl or music culture. 
Apogee Duetta Signatures...or pretty much any Apogee. If you cand find them.

Agreed that almost any, or most decently designed speakers can "disappear."  Though some do it much more readily and successfully than others.
A good bet is for the speaker to be time aligned and put in the room so as not to screw up the phasing.
I second georgehifi’s comments on Audio Physics and ESL’s.   I own ESL (X-Static) and the only other speaker I’ve heard that comes close and is musical is the Audio Physic Tempo Plus.

Also, agree that the room, placement, equipment, cabling, source all matter as you are listening to a “system” not any one Componenet.

I am chuffed to bits with mine an ex dem pair of Piega Classic 40.2. Superb ribbon tweeter which just gets the music right. I use these with valve amplifiers which really assist with the staging. Prior to these I found Living Voice did a reasonable job. However the Piega also pass the wife test which is important. 
Boenicke W5 can do this well. Also have impressive bass för being so small. 

I agree that Audio-Physics are also good at this.
EASY-PEASY:  Anything Magnepan SET-UP correctly with quality electronics.  (You only hear what you enter into them, good or bad.)

RE: poster who suggested horn speakers.  PLEASE listen to ANY properly set-up horn speaker next to a set of properly set-up Maggies of pretty much any era.  You may not change your mind, but I kinda think you will.  Be sure to listen to your favorite music on both.

Harbeth P3esr 40th anniversary with a good sub and near field listening has been what's floating my boat lately. Steve Guttenberg says they disappear more then almost any other speaker he's heard, he comments on them all the time on how good they are.
In your price range, Martin Logans.
You need to master set your new speakers regardless of what you buy.

I would highly recommend buying Salk Audio's Song3 Encore tower speakers.  Jim Salk sells direct.  He can then afford to build his speakers with the highest quality drivers.  The song3's deliver a bass extension of 25 HZ and are just incredible.  I will upgrading to these within the next two years.  I would suggest calling Jim Salk to discuss what speakers he would recommend for your space.  He is one of the most knowledgeable people in the industry and he is extremely honest.  Tell him Larry Edwards sent you.
Most high-end speakers will disappear in a proper room. Monitors more so than floor standers.
My $250 used and vintage Spica TC50 monitors speakers.  Wonderful in this regard. 
Joseph Audio speakers disappear and image with the best of them.  I also like ProAc and Vandersteen for these reasons, but there's just something special in this regard from JA speakers.  Also agree Audio Physic speakers excel in this area, and Avalon speakers also impressed me in this regard.  I think Verity Audio and Gershman speakers are also very good in these areas as well. 
Dynaudio, Proac, Harbeth. Setup and room are super important 
Dynamic drivers: Bowers Wilkins 703 S2 and 704 S2 , somewhat hi-fi ish sounding in most set ups but nonetheless are at least superb.... Nothing comes close at their price, up to the Rega Rs 10 at 13 grand and the B& W 803 D3 at 18 thousand .... They do take time to break in thou... at least 500 hours , but are fantastic .....
Rega RX-3 is great at $2 grand, as is Dali Epicon 2, simply superbly musical stand mount loudspeaker, I think they are 6 thousand new, but I ve seen them here in mint condition at around 3500-4500, also worth asking for a discount when buying new&demo units... The B&W 805 D3 (you can haggle with a dealer and get them new with about 20-25% discount off of their $6500 price tag, as I ve done for a friend of mine) will do a disappearing act like few are able. Very refined sound, especially if you have large library of classical works and know what live music sounds like....
Gradeint Helsinki 1.5, these may wow you, but are an acquired taste, which few  audiophile possess these days, with their penchant for boom and TSIK, and other pyrotechnics passed for "detail" and "transparency"...
The Eminent Tech 8bs at $2500 (plus $ 250 for almost required Sound Anchor stands) are one of the best speakers at any price, but they need lots of room away from walls (at least 3 feet) to sound their best (which is unlike anything you will hear at any price with good amps and proper bi wire cables).... But they are tall, somewhat massive columns, hardly WAF prize winner ;) however after listening to them pretty much everything else sounds sounds like a second carbon copy of music ....
I still use BW 801 series 2 and I have huge soundstage,but as mentioned in prior posts,set up time and rooms make a huge difference.Also have Roger's Studio 1m speakers and they also disappear quite well.Let's not forget the Amp, pre-amp set up that also makes that happen and what content you are listening to. All parts make the magic happen.
Spatial audio M3 turbo s. 
There is too many factors going on to just point to the speakers for the ultimate out of box type experience. Over the years I found Apogee to be the most open speakers i have heard, given plenty of room behind them and correct amplifier match is paramount. Look at your system as a hole, system synergy and room interaction is critical. Isolation is also critical as well as cabling. People can give you options but home audition is a must, there is no one size fits all, no rooms measure the same,

There are some really great speakers out there, what is your preference ?

Stand mounts ?
Floor standers ?
Electrostatics ?
Ribbons ?
Hybrids ?
Open Baffle ?
Actives ?

Have I forgot any ?
Long gone - Fuselier, Fuselier, Fuselier
Have you tried Reference 3A? I have the Grand Veena and love them. The reason I bought them:  Harry Pearson listened to them and gave them a good review. Their web site is:

Service is excellent - I have had a driver blow out. It was replaced promptly and at a very reasonable price.  And they are relatively easy to drive.
if You can find a pair of Avalon eclipse 
set up properly 
all  you will hear is the music 
Egglestonworks Emma Evolution is a great speaker. Vandersteen Treo will blow you away. Martin Logan ESL-9 is quite spectacular. I am a dealer for these. The most important person is you. It's your money, couch and taste...Happy listening.

If you'll consider used think about Thiel ,
read the Thiel Owners thread ( over 6,000 ) and see how much praise they receive from the owners , myself included .
My Reference 3A MM de Capos. Sweet!
From all the speakers that I have heard it is usually the monitor speakers that do the disappearing act best. The less MDF to rattle around the less the speakers reveal themselves. I like the Chapman speakers sound good, they are transmission line speakers and the usually cabinet rattling bass rear waves have an escape route that seem less obvious then sealed or ported.