Agreed with above. If you don't need a monitor and OS, you can build yourself an HD5850 Crossfire system for $1300. Phenom II x4 OC'd, 4GB DDR3 -> 1600, 1TB?, 885G, I donno.
Deffinetly, i have it and it runs awesome, although you may need to buy a new power supply or else your computer may crash when running games because i had to. I can run games like assassins creed revelations and dishonored beautifully