ive just bought a 1.8 20v non turbo on a 2000 plate for 900 quid with 128k on the clock n a nice set of wheels. cheap i thought its pretty slow compared to my cammed 2.0 8v mk3 but its a real nice drive and its dead comfy. cant say about mpg yet but im pretty happy for the money so far...
I would go for 1.8 turbo. I just gpt my first & its great plus i got it for 210. From where i work. I would deffo not got 2.0 gti as it is a fake gti. 115bhp is a joke when ky 1.6 16v azd gives 105 bhp.
I would save up a bit longer and get a mk5 gti, the only mk4 I would consider is the r32, I don't wish to offend anyone but 2 of the three mk4s I've experienced were so dull, only one had anything going for it and that was an r32. (I never owned any of those cars, one was a friends r32, one was a hire car on holiday as a teenager and one was a courtesy car)
I would have to say the Mk4 Golf GTI 20valve turbo is the best. Either the 150bhp or the 180bhp variant. This is the one to go for instead of the 2.0 GTI. So much more scope to modify. I am selling one now. http://www.ebay.co.uk/itm/VOLKSWAGEN-GOLF-MK4-GTI-TURBO-SILVER-excellent-condition-/331943887931