I would buy something that someone had spent a bit of money on converting for track use but was still road legal so there was no need to trailer. My reasoning is that £8K spent on a hot hatch that is still factory will not only be a compromise in the fun stakes but will also be money down the drain. Think about it.... would you buy a used Renault for say, £5K that had been someone's track slag?
Failing that I'd go for a much cheaper older car. But then, tinkering with the oily bits is my idea of fun.