Paid 1700 for mine as aTD, the td isnt a definate bad engine, its not good if abused, it can overheat very very easily when rad gets slightly blocked but if you really take care of it it can last a long time. In good nic its reliable, very simple and better than a NA diesel on the power front.
personally and this is from a good few years experience I would go
1) TDI - 200 is a cracking reliable simple lump, overheat it and yes the head gasket will go and head warp, change the cambelt regular or it gets expensive when it breaks, dont block the rad with mud cos its smaller than a NA or TD rad.....
2) NA - superb simple reliable engine, [!Expletive Deleted!] all can really go wrong even if abused, only prob is it is underpowered compared to the rest but get a good un and itll last forever.
3) TD - you may get a good one but for every good one there are 20 bad ones...if there are more than 21 TD's still on the road that is :), you really need someone knowledgeable to look at it.... crankcase overpresssure is common, cracks between cylinders in the head common but not always terminal...overheating a prob, worn turbo impellar grinding ally body into the air intake... worn turbo bearings...remove intake pipe and wobble the impellar to test.
Cheers Steve