I'm afraid the difference between a good one and rough one is huge on these cars. We'd expect to see a really good one at a dealer for almost £20k, while a good one for sale privately could fetch about £15k. One that's in need of some TLC is about £7k while a project... well that could be as little as £2500. Hopefully, these example prices will give you a rough idea of where yours sits - the next thing to do is look at current examples for sale and price yours accordingly.