Here's a trick I have used.
Not sophisticated, but believe it or not, it works.
Got buy some carpet. I don't care what color it is, etc...but it should be rather thick. Any Colour You Like, as it were.
Nail up 2X4's around the edge of your walls, right at the ceiling.
Cut peices of carpet so they cover the walls, but overlap the corners. They will hang 1.5" off the wall, leaving a dead air space between the carpet, and the wall.
The thicker the carpet, the better.
Nail or screw the carpet to the 2X4's with washers around the nail/screw, letting them hang freely all the way to the floor. Again, overlap the corners.
Basically, you've just sound insulated/isolated your studio for about $150 total (Depending on how much carpet you need).
(I've never done the ceiling, but I guess you could. I've always wanted to try that).
Those acoustic foam tiles look like shit (not that carpet hanging on your walls won't....), but they get EXPENSIVE quick.
Believe it or not, the carpet trick works quite well........not what you would use in a professional studio, but it is easy to put up, easy to take down, easy to change (if you don't like the color), and CHEAP.
Cut slits for the doorway (don't cut the doorway completely out, though).