Hmmm, tough but here's my suggestion:
Mobo: ECS K7VMA (On-board vid and sound, very stable board.) ($65 on pricewatch)
CPU: Retail Duron 750 ($50 or so on pricewatch)
RAM: 128MB PC133 SDRAM (about $25 at Crucial)
HD: WD Caviar 20GB ATA/100 7200RPM ($75 at pricewatch)
Modem: Cheap $10-20 Winmodem
Case: 300W PS ATX Case ($40-50)
CD-ROM: Cheapest brand name CD Drive you can find (probably $25-40 range)
Floppy: Generic Floppy ($10 or so)
But now for the monitor, the cheapest I've found is nearly $100, and the Printer, I saw a few in the $30-50 range but, none of them came with a printer cable. So you probably will need to spend $500 because you have shipping also, but this is my best suggestion.