I'll try to build a rig with a few 5830's and make it as cheap as possible, here's what I'm thinking about:
CPU - unclocked Sempron 140
MB - something on AMD 770 like MSI 870U-G55
Mem - 1 GB DDR3 1066 Mhz
Video - Sapphire Radeon 5830 1 or 2 pcs
HDD - second hand SATA 80 Gb
PSU - 500+ W
Some fans

Running caseless for a better airflow...
Critic is welcome.
Should I make any changes to maximize the performance?

I'm thinking about Sirtec High Power 650