Drew the Owens Corning 703 panels I purchased are 2ft x 4ft and 2" thick. They came in a case of 12 sheets for around $120 bucks from the local insulation distributor. In the front corners I actually stacked triangles from floor to ceiling that I cut out of my first case. I got 8 triangles out of each panel, each one being 2" thick. That took one case. However, you could just stradle the corners with 4" thick of material by doubling up the 2" panels and building a frame or whatever to hold them in place.
My wall and ceiling panels are 2" thick and address the higher frequencies. I still have 6 panels left in my second case, I plan to build 1ft wide columns for the rear corners with those.
The rest of the material I purchased from the walmart fabric department pretty cheap...My website shows some of the building progress if you check out the picture pages.
