Computer Base Unit for christmas! :)

Hi all, im looking for just a base unit computer for use with multimedia, like gaming, movies and general tasks. I want it to be quite fast and also something that is fairly easy to upgrade. I dont mind if its a refurb and im looking for a price of ?00-?50. There seems to be some pretty decent specced computers at pc world that are refurbs but they tend to come with low spec graphics cards and the psu's are not listed :/. Please could you help me find a system that will be reliable and is in GBP currency.Thanks very much,Sean