Felix79: Thanks for the advice, how would I check for rust under a body kit? I'm assuming getting under the car would be ideal, but if I can't then is there any other way?
adit: I spoke to my dad and thanks to ian332isport's very valid point of 10k avg. per year theory, he did accept it.

So as long as there is a good service history, 120k + miles should be fine. Thanks for the boot idea, I hadn't thought of it..
bump: I have been looking for an i or iS but all I've been finding are a lot of E30 325i out there, when compared to the amount of 318i or 318iS models. Saying that, I don't think I've found more than 1 iS for sale so far.
magpie: I live in London, so I think about 40 miles away would be the furthest considering I would have to take my dad who can be very busy. If the car is near to me, I would take my cousin who's a mechanic..
Finally.. when buying the car how would I be able to check the engine's state? If I didn't take a mechanic? I've been reading up and I know there are certain items which need to be changed.. such as the cam belt at 50k? (I hope I'm right in saying that.. ):?