Well, the "Cheapest" way would be to take an existing corner of the room, put up some hooks to put up on the ceiling and go out and get a heavy blanket and hang the blanket so it forms a box. The harder way is to go out and buy 2x4's and some Sheetrock, and get get to work. What did you have in mind? Another really cool idea is the eS Reflexion Filter, may not be the best for guitar, but that thing is great for vocals!