Rigid fiberglass is probably your best bet. ScottMayo, a member here, custom makes them very reasonably.
I did make my own. What I can't do is sell them to other people - my business pricing is not structured to handle insurance costs for that. Instead, I tell people how to make their own traps and other devices themselves.
What you are looking for is the single simplest trap in the world, and you can build it for a fraction of what the big boys charge. This will build a trap that stops mostly HF frequency, and is good for 1st reflection points.
Start with some Owens Corning 703 or Roxul RXL 40, in a 2" thickness. These are the guys for it:
http://www.spi-co.com. In Canada, contact Roxul for their distributor. A 2'x4' sheet is what you want - they sell them in packs.
Lay a sheet of it on the floor, and build a wood frame around it, out of cheap pine 1x4's, with the 1" face of the wood against the floor all the way around. A 1x4" is about 3.5" wide, so the wooden frame sticks up higher than the thickness of the fiberglass, by about 1.5".
Screw the frame together (I like adding L-braces inside to keep it squared) and then spray a little 3M "77" adhesive along the wood where the fiberglass touches, all the way around. Allow to dry for a few minutes.
Now get a piece of colored burlap, 3'x5'. Slide it under the frame, more or less centered, and spray the outside of the wood frame, all the way around, with the 3M glue. Pull up the edges of the cloth against the sticky sides of the wood, pulling it tight as you go.
Volia, a simple trap. Cut away excess burlap, and mount it on a wall so that the 1.5" air gap is against the wall, and the flat burlap surface is out to the room. This trap won't do a lot of bass trapping, but it efficiently eats the frequencies that affect imaging the most, so it works out well at 1st reflection points.
Commercial products do it better, and there are all sorts of changes you can make to this trap to get different effects. Note that 2'x4' is a little small for a 1st reflection trap - but putting 2 side by side is often plenty.
Pine (you don't need fine quality because none shows) is relatively cheap, and OC 703 isn't bad if you buy a bunch. A power saw capable of straight cuts, a drill, a power screwdriver, and you're there.
Note - the Roxul is mineral wool, not fiberglass. It's not as tough, a little denser, and ecologically friendly. Whichever you use, wear a dust mask when you mess with it.
Keep in mind that a normal "cubic" room with 2 speakers has 12 reflection points. You might or might not want to go after them all; the effect varies.
