Don't listen to Steve - he's about the only ex-Roadster owner I've ever found who wouldn't want another.
Yes they do leak - but most leaks can be fixed.
Yes they handle the mileage - I do 18,000 a year in mine and it's fine. Bear in mind they're small and fairly noisy - have a drive and see what you think - they're not for everyone (as Steve is testament) but most fall in love within minutes of starting the engine.
Servicing is every 7000 miles and they are A/B/A/"C"/A/B/A/"C".
I now do all A services myself and it costs me about £20 in parts. B & C services I leave to a specialist as it involves removal of the rear panels, but they come in about £200-£250. If you don't want to do an "A" yourself, a specialist will charge about £100.
£3500-£4000 should buy you a decent one. I'd be wary of anything sub £3k and walk away from any where there is a hint of any electrical gremlins.
Visit http://www.roadstermodelguide.co.uk/...ers_Guide.html and www.theroadster.net for everything you need to look for when buying a car.
Also given your location, I'd suggest giving fudge a call (www.fudgesmart.co.uk). They're a trusted smart specialist near Newmarket and they often have Roadster's for sale. If you buy from them you can be sure you are buying one that's been properly checked over.
2004 Roadster-Coupe SB2 Brabus
2005 ForTwo Brabus Numeric
2014 Skoda Yeti 4x4 DSG
ex 2002 City Coupe 600cc Pulse
ex 2003 City Coupe 700cc Passion