depends if you want the whole lot or just the base. TBH nowadays places like Dell can sell you a PC just as cheap as you could DIY it for!!!

you could build yourself a PC for about 300quid even with all new components, and it's be more than adequate for anytihng other than new 3d games.

www.ebuyer.co.uk theyre nice n cheap

or www.scan.co.uk theyre cheap too (and often do good bundles for barebones systems)