In your position, I'd be tempted by a Mazda MX-5. Your budget will get you a third-generation model (www.honestjohn.co.uk/carbycar/mazda/mx5-2005/) with the 2.0-litre engine, producing 160PS and hitting 62mph in 7.9 seconds. It's not the most powerful car you could buy for the money, but it's a lot of fun and will also be cheap to run. If you'd prefer a bit more practicality, consider a hot hatch like the Volkswagen Golf GTI.