Hi Jon,
You have a few options really, for that kind of money you'd be able to get a real "minter" and probably do stage 1 mods to get her the way she should be.
The other alternative would be to buy one of the higher mileage ones you see about for 12-15 k then spend another 10k on bits and bobs to get a really sorted car.
It depends on what you want really.
another option would be to buy an already modded car with big brakes etc.. you could probably spend up to 25k on a fairly well sorted R33 and be ready for the track/dragstrip.
It really depends on if you want a really tight car that you won't have to do a thing to. Or if you are planning extensive modifications which require rebuilds anyway then the condition of the engine/turbos is not really too important as you'll be ripping it all out and starting afresh..
For track work I'd recommend bigger brakes, these seem to make more difference than 100 BHP would to your laptimes. but then bigger brakes and an extra 100 ponies and you have it all !!
sorry about the waffle.
/Steve
Decide what you want to do at this stage and save yourself a fortune. If you go for modifying try to have an action plan so you only have to buy parts once (where possible) an example would be getting steel internals for the turbos, then deciding you want more power and buying bigger turbos..same for intercooler,injectors,ECU's,suspension.. the list is endless.