Hi,
looking at newegg here's what I've used to get approx. 700-800Mhash/s, and power requirements around 810W, so you can still attach some 3W LED's to visually track hash crunching.
Server chassis ARK 4U406 Black 1.0mm thick 4U Rackmount Server Chassis - $86
http://www.newegg.com/Product/Product.aspx?Item=N82E16811128064PSU Rosewill Xtreme Series RX850-S-B 850W Continuous @40°C ,80 PLUS Certified - $100
http://www.newegg.com/Product/Product.aspx?Item=N82E168171820722x GPU Dual Fan Design PowerColor AX6950 1GBD5-2DH Radeon HD 6950 1GB 256-bit GDDR5 PCI - $250
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131389&cm_re=6950-_-14-131-389-_-ProductMotherboard MSI 870A-G54 AM3 AMD 870 SATA 6Gb/s USB 3.0 ATX AMD - $105
http://www.newegg.com/Product/Product.aspx?Item=N82E16813130275Kingston HyperX 4GB 240-Pin DDR3 SDRAM DDR3 1600 Free flash drive w/ purchase, limited offer - $46
http://www.newegg.com/Product/Product.aspx?Item=N82E16820104244 AMD Sempron 140 Sargas 2.7GHz Socket AM3 45W Single-Core Processor SDX140HBGQBOX - $38
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103698Total of $875, since i didn't calculate flash memory or HDD since if you're lucky you can get one 4GB flash drive along with the DDR3 memory mentioned above. No DVD too (who needs 'em anymore?).