You may want to check out the following links. If you're in to simple DIY you can equal or better about anything commercially available.
http://forum.studiotips.com/viewtopic.php?t=536
This one illustrates the relative cost of room treatment normalized to the effectiveness of the absorber.
http://forum.studiotips.com/viewtopic.php?t=534
http://forums.studiotips.com/viewtopic.php?t=535
http://www.bobgolds.com/AbsorptionCoefficients.htm
TONS of info here for those so inclined.
http://forum.studiotips.com/viewtopic.php?t=536
This one illustrates the relative cost of room treatment normalized to the effectiveness of the absorber.
http://forum.studiotips.com/viewtopic.php?t=534
http://forums.studiotips.com/viewtopic.php?t=535
http://www.bobgolds.com/AbsorptionCoefficients.htm
TONS of info here for those so inclined.