Chorus recommended ua-acoustics for a really cheap solution. Be aware that these are just foam panels. They are NOT the same thing as GIK panels which use fiber material similar to Owens 703 and the like. I have tried foam panels before and they really don't do what you want them to do. They don't absorb all frequencies and I actually had worse results with foam panels.
GIK Acoustics really is the cheapest "GOOD" solution here. There is a company called ATS Acoustics that has panels slightly cheaper than GIK, but they use a hard-back panel frame (essentially a 1/4" piece of plywood on the back). This is not the design you want because I have found the hard-back will resonate with the material and create more echo/vibration.
The 3lb 703 is excellent choice to work with because it is super light and it also does not sag. I wouldn't recommend the 6lb 703 because it's a lot heavier and doesn't really do much different. For my room, I just took a 703 2x4 panel and wrapped with with Guilford of Maine black fabric. I just used spray glue on the back side to hole the fabric closed. I don't made frames for my panels, but I also don't hang them (I just sit them on the floor/wall or on top of a bass trap agains the wall). You can make frames if you want. It's really not difficult. Just get some light weight pine 1x2 from Home Depot and cut them. Then glue/nail/screw the frames together and inset the 703 into the middle. Then wrap with fabric of your choice.