Change the case to something like the CM HAF 922, CM 690 II Advanced, or Antec 902. And you should really get a better power supply. Seeing as you can't crossfire on that board a 500W unit from Antec, Cooler Master, Corsair, OCZ would be fine. If you want to be able to take the PSU into your next build then a 650W from a good brand would be fine as well.
The only other way to save costs is to get an AMD Phenom II X4 955, and then you could spend less on a single PCI-E slot mobo or the same amount on a crossfire capable mobo.