Vehicle worth is hard to determin. While he may put $ 3500 in the engine and some more in the transmission if it goes out, he should be good for another 100,000 plus miles. If he looks at a used vehicle it will have lots of miles on it.
I drove a car that had almost 200,000 miles on it before I was looking to trade it in. I had driven the thing way past the point the timing belt was recommended to be changed. As it would cost what if not more than the vehicle was worth, I was gambling the belt would not break before I bought something else. I bought a new car and kept the old one as someone at work wanted it. I sold it to him at the price ($ 500) I was going to be allowed on a socalled trade in. He knew that the belt was way over due because I told him. Not sure what he did with the car as he was actually buying it for someone else.