AMD Sempron Palmero 2800+ $86
MSI K8N NEO3-F Socket 754
NVIDIA nForce4 ATX AMD Motherboard- $75
Giel Value ram 512MB(2x 256)-$45
Video card- Ati radeon X300 SE HM-$55
Hard drive- SeaGate 80 MB 8MB Cache 7200RPM SATA hard drive-$65
Cd Drive- NEC Dvd burner-$50
Case Antec Case with 300 watt power supply (SLK2600AMB)- $60 dollars
Adds up to 436 dollars. Without monitor/keyboard/os/speakers. If your really worried about price, then you can make cuts in these areas.
The video card can be downgraded to Geforce 6200TC 128 MB. Hard drive can be 40 or 60 gigs. Cd drive can be a low cost one that is 40 dollars. Those cuts will roughly save you 40 dollars. With this setup, you will be able to overclock slightly. Yes, you said you wouldn't be overclocking, but free performance is hard to pass up, and it will speed things up. You can also play some moderetly speced games on it. Nothing big like doom3, but wow on moderate settings will run pretty well.
If you really want a cheapo computer, get a mobo with onboard everything that will retail for 60 bucks, a sempron 2600+, which goes for 70 bucks, a 40 Gb hard drive, a cheapo case, and 512 mb of some cheapo ram.
Will equal roughly 270-290 dollars. Then get a Crt monitor for 100 dollars, and a keyboard/mouse combo for 15. That will be around 400 dollars, but not including the Os.
Finally, there is a third option. Get a 400 dolalr dell.