I really don't think you should go cheap on a case (especially a server case). To get one that holds enough hard drives without having to use those cheasy adapter brackets, look at ones like
this. That will give you plenty of room for hard drives.
BTW, looking to get any case worth a damn for under $50 AND be server class is asking WAY too much. When you say 'server' and room for 6+ hard drives you're out of the $50 range. Hell, looking to install 6 (or more) hard drives in any case that's worth a damn (and not chew up some 5-1/4" bays) is going to cost you. Then again, if you don't mind slicing your hands up during install, or having a case that wobbles when you walk past it, then go ahead and be cheap.
Just remember, as with most things in life (and the real world), you DO get what you pay for. Pay cheap money for a case, and you're getting a cheap case.