Call a machine shop and ask him how much to bore the engine,and press on new pistons to good used connecting rods. You will need to get the crank replaced or turned and a valve job. He will give you a price on labor and parts including gaskets and oil pump.
After you get this done you and your uncle will need at least two complete days.
You should be able to get this car for less than $1000.00.
It is always cheaper to get a good car with low mileage. You pay more on the front end but much less on the back end.
This salesman is taking advantage of you take your mother with you and let her be tough with him. This means saying no until he drops the price.