Build it yourself! It's not hard!
Get a DFI Lan Party Pro875B with any Intel socket 478 CPU (min. 2.4Ghz), 1 Gig of memory (or more), an Albatron Ti4680 graphics card, and an Antec TruePower 550 Watt power supply with the case of your choice. You could easily keep that in your price range while maintaining a system you could upgrade as time requires.