If you can find a restored MPi that might be better. As carthorse says, good MPis will either have really low mileage or have had lots of bodywork done - mine falls into the latter category! It's on 66k and there's no rust on the body at all, so there are solid MPis out there, you just need to look hard and be prepared to wait. That's why I like the idea of a stop gap car - you may have to wait 3 months + to get a really nice MPi at the right price. If you can get a solid, restored one, and you look after the bodywork and keep it in good order, that will cut out the main expensive area on a Mini. The mechanicals are cheap to fix compared to a modern car for the most part, it's the bodywork where things really get expensive. I always keep mine waxoiled underneath, keep the arches clean, polish and wax etc. The previous owner was very fastidious though, he even waxoiled on the inside, around the windscreen seal!
What sort of money is required to buy the condition you describe?
I'd say that £6k should easily get you a really tidy, restored MPi with great bodywork if buying privately. But you'd need to look it over thoroughly and be 100% sure that the car was solid before you bought it.