Before treating my studio I looked at all the options. Building my own traps was a lot cheaper than buying them. Also, you'll see foam traps being hawked all over the place and yes, they are cheap. But they do not work to attentuate anything under 200Hz, where most of the problems are. Panels that are dense do the job, foam does not. High density Rockwool is the best. The biggest problem in any room, especially square or rectangular ones, is in bass frequencies. Tackle those and you're on your way to a good sounding room. Then, using the "mirror technique," you finish up by throwing up some foam panels on the walls. Rugs or ceiling treatment also helps tighten things up. There's a great, free program; Room EQ Wizard, that's of great help dialing things in.
I have a 20' x 15' home theater. My only treatments are a thick almost shag dark rug; a piece of that rug on the back wall to minimize slap back, and dark grey walls and ceiling to minimize light reflections. I should put something on the ceiling and certain walls since I can hear sound reflection depending on volumn, but prefer not for aesthetic reasons. I can't have the wall corners attenuated due to my dual array speakers. It would defeat their purpose of providing a deep sound stage.
FYI, I got tired of front directional speakers years ago. Looking for that elusive stage depth I tried Bose (not impressed), went to Ohm's (too short), Mirage towers , and finally Def Tech because of their powered sub-woofers and a more neutral tone. I now use the Mirage towers for the rear surround and although I could initially hear the tonal difference between them and the Def Techs, I don't notice it anymore. Anyone who has heard my setup are stunned by the realism. Don't need no stinking 7.1 or more.