Check out
www.honestjohn.co.uk for excellent advice and information on new (and secondhand) cars.
You can push for big discounts at main dealers these days so your money may stretch further than you think.
The Mini ONE can easily be chipped to boost power to Cooper level, if you're interested. The engines in both models are identical save for the difference in engine management chip programming. Personally I'd go for a Cooper S convertible in black, but I'm biased, and it's out of your budget.
If practicality is no issue then might I suggest you head down to your nearest Honda motorcycle dealer, and pick up a VFR800 or FireBlade, giving you loads of cash to spare for essential clothing and accessories. Again, I'm biased here too ;-)