Nvidia GeForce GT480 ($450-500)
Intel i5 750 ($200)
Asus P6 Motherboard ($200)
2GB DDR3 RAM ($50)
Noctua Air Cooler ($50-100)
Antec Case ($120) can't remember exact model #....
Total: $1070-1170
Prices are just estimates, but that would get you 30+ fps at your 1600p resolution.