s4marsh: my mates currently building a locost, which is a general name for the build-your-own-lotus7-type-car-from-a-book things.
Its really not possible to do it for £250 these days, the donor vehicles fetch more than that alone, and the costs of all the parts are pretty high.
Also doing a single donor build makes quite a lot of compomises, so when you start changing things to make them better it starts getting a lot more expensive.
He's using mazda MX5 uprights for instance, and was also planning on using the MX5 rear diff, so he baught an MX5 shell for all the parts, turned out the diff wasnt going to be strong enough for the power he wanted so he had to find a ford cossie diff, which is ~£200 on its own. He had a volvo T5 engine, decided to go with that, but then had to have various bits machined off the sump and a custom gearbox bellhousing welded up to make the volvo lump to a BMW gearbox.
He's probably spent a grand or two already, and doesnt even have the frame built.