There's no doubt the BMW M635CSi is a classic in demand. At a recent auction, someone paid more than £100,000 for one (classics.honestjohn.co.uk/news/auction-news/2017-0.../). But that was the exception rather than the rule. We can't offer a specific valuation for your car, but we can give you some guide prices. Expect to see top end cars on a dealer's forecourt for £45,000 while good, unmolested private ones tend to sit around £25,000. The best thing to do is research the market - find a vehicle that's similar to yours and price it accordingly.