I would like to build a back-screen for a drum kit (highly reflective stage etc.) Currently I'm thinking of 6 2'x6' panel screen for the back, and I'm currently got a few materials suggested involving: MDF Plywood, Plasterboard, fibreglass -- insulation type. carpet and/or underlay.
In my studio, I use 2'x4'x4" slabs of mineral wool wrapped in acoustically transparent fabric (can blow through it). I've spent a little more on ready made covers, but the last half dozen I made I bought fabric and glue at the fabric store - less expensive but more work involved (have to wrap them up like xmas presents).
I use these traps in the corners as bass traps and at first reflection points as broadband absorbers - they work great.
The mineral wool was $2/square foot, and the fabric was $10/yard. It's about 1/3 yard per trap, so the per unit price was about $20.
If these are stationary, then you'll need something to hang them with. I use standard shelf brackets on the bottom, and some strapping secured to a wall anchor near the middle top to keep them from toppling over. I leave some space between the trap and the wall to improve acoustical coefficients.
If they need to be portable, I'd recommend some framing and stands to make them more durable and flexible with regards to their placement. If I were framing mine, I'd start with a simple picture frame design using 1"x4" glued and spline mitered for strength. I'd secure the traps within the frame by strapping across the corners.
I made a great set of absorbent panels out of plywood and then covered them in old carpet. If you are really determined drive around and look for someone doing house work and see if they are ripping up an old carpet you may even be able to get some for free. You can either put the carpet flat on the wood (staples or small screws work well to hold it on. Or if you have time you can ruffle it like a wave (about 4-6 inch waves to maximize how much absorbent surface you have.