I recently embarked on a build to see how cheap a reasonable PC could be. Dont laugh but my budget was £250!
The specs are:
Processor-AMD Athlon 2 X2 250
Case-Antec 200 V2
Power Supply-Antec VP350P
Optical drive-An old Samsung IDE DVD drive i had lying about.
HDD-Undicided (open to suggestions)
Monitor-second hand 15" for £20
Graphics-an Ancient PCI from about 1997! Until i have enough money to get a half-decent one