As LeanneNCharlie said, you can rebuild the engine for around 350 quid, (about the same as what i did it for), if you do it yourself. If your thinking of having some1 else do it, thats gonna be a lot of labour and would be cheaper to go for recon. Also after you've rebuilt it how longs it gonna take for something else to go wrong? As has been said they do run hot and from an engineers view the engine is not designed to take the extra stresses assosiated with the turbo. That being said, how is the turbo? if the engines been breathing heavy is it all gunked up or are the bearings on the way out? all things to concider.
imho a tdi is the way forward, altho the initial pay out will be more you will get that back in mph, torque, power, and not having to keep replacing bits and pieces. I did it on a very tight budget and the only thing i regret is not having done it sooner.