Standard ATX mobo
CPU, I suggest AMD for cost saving. (I've a Phenom x4 and never had problems)
Great budget GPU: Radeon HD 6770
8 GB RAM
7.1 Sound card
rounding to 100, 160, 100, 40, anywhere from 15-100 = ~450
salvage what you can from old PC: Case, HD (though a fresh OS install is recommended), Disk drives (bluray if enough $$)