Passive soundbar

Looking to de clutter and move my current second system to become a third system and in doing so am looking to replace my pioneer elite Andrew Jones Dolby Atmos L/C/R towers and center with a passive sound bar being driven by marantz 7007 receiver. I have multiple zones and things hooked up so a powered soundbar is not an option. Guessing I will need to add a sub or two as well given physical limitations of the sound bar.  I have about 43” width and somewhat varying height and depth let’s say 6 to 8 inches high and 7 deep. Not looking to break the bank but doesn’t seem like there are many cheapish options out there.  Am I missing a quality speaker somewhere ?  Would like to keep under $500. 
I don't think there is anything out there which is that cheap.  Probably your best bet is to get three matching "center channel" speakers and line them up.  The other problem you has is that your width is limited to about 43".  Most center channels are at least 20-21" which would require about 63" width.

You could try to find something small, such as Cambridge Audio SX-70 center channel speaker, which is 14-1/4" wide (three would require 43" exactly).  They are $180 each from Crutchfield.

There's only one truly passive soundbar that I know of.  Legacy Audio has a "Soundbar" passive speaker, but it's 48" wide and going to cost around $1300-1400.
If your Marantz 7007 receiver can setup without a center channel speaker, you can get two matching "center channel" speakers instead of three, use it as left and right front speaker as @auxinput suggested.

Interesting suggestions. I see Dayton audio has a relatively cheap center and 10” powered subs for just a few hundred- anyone have any experience with those?
I have used Dayton parts (such as a full-range or a woofer).  They are actually very nice for the money.  However, don't go for the ultra cheap stuff.  If you are looking at the Dayton center channel speakers for $50 or less, they are pretty much crap.  Also, the packages that have sub and speakers for $300-400 are also going to be crap.  The idea that you can get more product for "less money" is not a valid one.  In the end, you get what you pay for.
Yep fully aware of the get what you pay for!  The system that’s impacted is a super casual-need-better-than-tv-sound with occasional two channel as background to fill a large space (48x16).  Looks like monitor audio and def tech also have some passives. 
I have only seen these as kits from Parts Express.
Parts Express does sell a number of pre-built center channels and sub/speaker packages, but they are all crap stuff.

The Parts Express "kiits" are actually pretty decent.
For only $299 the Yamaha YAS-209 may get the job done, and it comes with a wireless sub.  CNET Editor’s Choice and several Amazon customers were impressed with its sound versus competitors.  FWIW, and best of luck. 
@soix - he wants a passive soundbar.  Not a normal "powered" soundbar.
I can make it , just take out amp from my regular