Maybe you should lower the initial price to $3,000 and count on putting a couple thousand in during the first two years. They're always going to need some kind of repairs at that age. Put some good tires on it (Michelin), tighten up the front end and align it. Do the brakes for sure. It will need a battery and exhaust soon enough. The air might need leaks repaired too. If there's money left after that, touch up the body. That ought to be safe & sound and last you for a while when you're all done.
I'm thinking of going the same route for my son's first car/ truck. It will be a full size V8, automatic and most likely Ford since I've had great luck with mine. The Fords purchased at the shop I work at each went over 200K during the 80s and early 90s. I'll be talking to my mechanic about how the different engines and trannies held up for that vintage first.