It's been up for ages because it's expensive, which means one of two things. The guy isn't being realistic and won't listen to offers, or he hasn't had any offers.
If it's straight, in as good shape as it looks and you want to keep it then offer him £3,5 to £4k, unfortunately you won't get it for anything less than that but, for that money it needs to be tip top. You'll get some money back for the wheels, just need a decent set to put on it.