The cheapest case is probably the Fong-Kai FK-603. Read the anandtech review for info on it. Im getting it in the next month from Directron.com. Its cheap and has cooling that rivals the huge Addtronics cases.
The case Da Whip pointed out is a very nice case for the money, I have the mid tower version for my wife's system and it is really roomy. I have an Inwin Q500 for mine since I needed a full tower to fit the watercooling sytem and I got this case for $95 w/shipping.
No Luck, That case looks really good. I like the swing out side panel and the lockable handle. They also had it in black, now that would be da whip.
p.s. Don't get anymore fans w/ case, order some Panaflo's or Sunon's, very good quality(fairly quiet). A 120mm for Blow hole,ETC.