Never cheap out on a case. I almost bought a $40 case + PSU for my new rig until seeing people mention the genius behind entrusting $1000 worth of parts to a $20 no name PSU. Even then, I only got an Antec SLK1650 for $80 which is a nice case, but really cramped (note to self: learn to read dimensions and define mini). Anyways, other than a quality PSU, a case that's been well designed for 'use' and spaciousness is really worth it.
Like others said, if you want a budget quality case, Antec SLK1650 or 2650 models are good, but really cramped inside. Their 350W Smartpower is pretty nice and quiet, but lacking on the 12v rails. Personally, I'd go with the 2650 though due to the extra features and the door on the front. I originally didn't see the need for it, but 1 screwy RMA later, I now have an ass of a front bezel. ~Contacted optical drive company, took 1 month for them to ask for an address and them to ship the bezel. Now one month later, where the f*ck is my bezel!~