ATS Acoustics is another place where you can get the parts to make your own treatments for less.
If possible, I recommend picking up
this book; it has information that you can use in treating your room as well as to make your own devices.
Depending on the characteristics of you speakers, you may not need absorption at the first reflection points (if you feel it's needed, I recommend using 3"-4" material, as 2" material is less effective below about 500Hz). But in any event, the best thing you probably do to start with is bass trapping.