Honestly the bare minimum I would go on a case is a Fractal Design R4 which is about $90-120. You run into a lot of dumb problems with cheaper cases (poor cooling options, no dust filters, poor cable management options, etc). I would suggest increasing your budget to get something that will keep you happy for awhile. Personally I have a Silverstone FT02 which is a solid case, but I have built plenty of systems with the Define R4 and it is probably the best for the money.