Well for a system that will almost max crysis it will probably cost you 10 grand about.
For 500, you could probably get a cheap AMD dual core system. Like a 4000+, 2gb ram, and a 8600gt. That system will probably play crysis on low. The price doesnt include the monitor.
Save some money.
P4 2.4GHz, 1.5Gb, 40Gb.
PowerBook G4 867MHz, 1Gb, 60Gb.