I've alway bought from friends or people I know. Most I have ever paid for a car is £300 and that is the one I still have after 5 years. Most of my cars have been free or under £100. One of the best was a Granada Scorpio 2.3 cost me £25 , I found a £15 wine voucher in it and it had £40 worth of petrol, when it broke down after 6 months I sold it for scrap for £75.
You can have the cars HPI checked, this will show if the car has ever been involved in an accident that the insurance companies got involved with and also if there is any outstanding finance owing on it.
Hang on, you had a car repair business ?