Does his sytem need everything (like Hard drive(s), video, sound etc?) If so, here is my best:
Thes prices do not include shiiping costs...
AMD Duron 650MHz $43
FIC AZ11 Duron 133MHz FSB 3D Video Motherboard $88 Can be upraded later on with faster video board....
ZEUS 128MB PC133 SDRAM $43
Creative SB PCI128 $23
15GB Quantum UDMA/66 Hard Drive $91
Delta 52X CD-ROM $26
3Com USR 56k v.90 Winmodem PCI $26
Mid Tower Genica ATX Case $17
Thats about it cept monitor, comes out to $357. That is over his limit but maybe you don't need all that hardware..
www.pricewatch.com is where I pulled the information
Good Luck !