Room Treatment, Panel Sound Diffusers

So I am setting up a third sound system in a spare bedroom.  I want to really get the walls and perhaps ceiling treated for optimal sound.  The bed will be taken out.  I will put in high quality duplexes like the ones sold by Cullen Cables.  However, there are a bunch of different sound diffuser panels with many being quite expensive.  I am going to do the install myself so nothing too complicated.  Looking for advice on the type of wall treatment that works but won't break the bank.

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The bargain/high value approach is a combination of Owens Corning 703 acoustic panels and Synergistic Research HFT. OC703 is cheap and easily cut to size with a knife, then all you do is wrap with fabric and presto, $500 acoustic panel for $20! This material is absorptive and very effective so a little goes a long way especially if used in the corners like this 

HFT don't work like conventional old school diffusers but they do make a huge improvement in clarity, detail, and imaging. The ones made for speakers and the ones made for walls all work the same, so if you don't want them on the walls you can still do the speakers.
+1 millercarbon.
However, if you don't want to DIY, I used a product called Primacoustic.
They were purchased from Sweetwater Sound. Treated all four walls plus the ceiling in a dedicated room.
Placed panels at all first reflection points, plus others at random.
Used system setup guidelines from Jim Smith's book Get Better Sound.
Improved the sound more than anything else.
Very happy with the results.
The room and the setup will give you half of the sound you will hear.

“Looking for advice on the type of wall treatment that works but won’t break the bank.”

Call GIK Acoustics, their acoustic panels are quite inexpensive once you consider the free professional advise and finish. If you want panels that looks like they were made in your garage then go with Owens Corning :-)

I did my entire room - 15’D x 30’W for $1500 / 20 acoustic panels...that’s $75 per panel.
Many thanks for the replies!  I did get one message questioning why I just didn't do a Google search for acoustic panels.....
For $100 per 4 x 2 ft panel I’d easily go with GIK as it will include a wooden frame and diffusor which is really advantageous compared to straight Owens Corning absorption. You could never make this for $20 per panel, they will be perfect in presentation and identical, and look nice with options to tailor to your aesthetic.

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Ditto the GIK recommendation.  I just redid my room with their product.  Good advice, good products and very affordable.  Their 244 panels are excellent as are various diffusors.
What is your sources?

I have acoustic panels from,

in a small bedroom with a floor stander. Look at my virtual system. If not for the fact that 2 of my sources are analog, SACD, tuner, I would not get the panels from these guys. The panels do the job but in an all-digital setup that is not how I would do it.

I am playing some ZZ Top via a digital stream right now at 75 db. Sounds fabulous in this small room. 
Just FYI, OP, treating a room is not done well 1 panel at a time.

You need to get a critical mass before you hear much benefits.  2 Panels for instance are unlikely to do much alone.
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Well there are a lot of questions to be answered.  How big is the room, what kind of speakers (monitors or floor standers for example).  It will most likely need some corner bass traps.  Listen to it without a lot of acoustic treatment before you go forward.  I have used acoustimac with mostly excellent resutls.
+1 Erik_squires. ATS Acoustics in Piper City Illinois provides ready made panels and DIY products. I have purchased DIY from them.
In a small room absorption is better than diffusion. Acoustic panels behind speakers and listening chair and at reflection points. Bass traps in corners. 
Again, thanks for the suggestions, vendor recommendations, and overall advice.  Much appreciated.