I'd check out fccuk for features of each car and a buyer's guide, I don't think there's one on this forum? (maybe a task for the coupe moderator, Sammi

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They can be had for as little as £1000 but I'd budget 2500-3k for a decent example. Buy on condition and history, NOT mileage. Plenty of low mileage dogs out there, and they like having their legs stretched. Ask the owner about oil usage, they normally take about a litre every 1,000 miles or so, sometimes they don't, but if the owner shrugs and doesn't know, that's not a good sign. Look for servicing at a reputable specialist if possible, powerfiat, motormech etc.
I'd recommend at least £500 set aside for jobs that may pop up after you've bought her, don't spend every penny you have on the car alone. If you buy a nail, you can spend a couple of grand easy on these, they can eat money like you wouldn't believe. Check for white smoke from the exhaust after it's been idleing a while, could be the turbo or seals on it's way out.
They aren't cheap cars, they are to buy, but not to run. That's why there's so many about that are cheap - they are bought, poorly maintained and sold on. Be careful, and I'd see at least three before you buy, so you get a feel for what's decent and what's not. If possible, take somebody along that knows the coupe fairly well, perhaps a current (or ex) owner.