Not all antec cases are so expensive. I've waited and gotten both mine at Fry's electronics or Fry's.com for $30 or less after rebates. You just have to be patient and wait for deals. I also use slickdeals.net, which lists links to many electronic items. So far, I've gotten 3 rebates from antec totaling $125.
The Antec 900 will perform better then the Centurion, but having friends with each of those cases, I would say that the Centurion is still a very good case, especially for the price. The Antec 900 is HUGE, so if you would want to move your computer around a lot, it wouldn't be too good of a choice.