Dunno, up to you man. you got 750+ posts here, you should know the basics
£50 is what I found plugging it in the auction site. maybe it can be had cheaper, maybe not. do you like the computor? does it still do what u need it to do? If so, then I would PERSONALY say repair it and keep it going.
If however, these last few years its become slower and slower and your glad to see the back of it, then flog it and get yourself a new pc.