CPU
http://www.newegg.com/Product/Produc...-225-_-Product
$232
MOBO
http://www.newegg.com/Product/Produc...-189-_-Product
$70 (this can actually do 1000Mbps ethernet, lol)
RAM
http://www.newegg.com/Product/Produc...20(2%20x%204GB)
$160
HDD (didn't say how big, but let's assume 1TB)
http://www.newegg.com/Product/Produc...20and%20higher
2x $70 (need 2 for RAID)
=$602
oh god my estimating skills are awesome, i should be a contestant on the price is right
i guess you'd need a case and PSU too, but since you don't need it to drive a gfx card you could either cannibalize something from a flea market or get a $20 bare-bones case w/ power supply.