Cheaper case = Coolermaster CM690 (around $100)
CPU = Can easily get away with a E8400
Do you already have the 9800GT? if not get a HD4870
I play crysis well on my system.....:
Q6600 @3.6ghz+
2x1gb Crucial Ballistix 6400 @ 1066mhz usually (can go to 1200+
Had 2xHD3870 in crossfire
Asus...