Finding a good case with design for under $75 is no easy feat. Especialy if you want a PSU with it. Also the more watts the better is not entirely true. Yes more is better if you have alot of things running from it, but you also have to consider the PSU stability, its rating on the 5, 12, and 3.3 rails, its conversion efficiency.
You also have to conisder the cooling potential of the case. I say spend some more on the case since it is the one component that you will always see and will be the last you upgrade if you ever do.
I went through 5 cases untill I found my Sonata, and even now I am eyeing the SLK3700AMB, but enough is enough, spend too much money on cases
One sugestion I would make is to get a case with either a crappy PSU which you will not use or one without, and get a PSU when you get everything else. The reason I say this is because PSU are starting to come out with connections for SATA, but not every one has them, and you do not want to deal with converters. Also Antec Modular PSU are looking quite interesting