There is a range, fair, good, very good, excellent... no car that old is going to qualify for very good or excellent. Since it does need some mechanical work off the bat, you're looking at the fair price, and again, I'd start with that, minus required repairs as the starting negotiating price.
Odds are you will never buy another car from this person again, and they will never want to deal with you again, so there is no reason not to start negotiating from a lower price, and you can always concede to a higher price later. Figure out the total price you're willing to pay, including taxes, and registration, and be willing to walk away if it can't be met by the seller. If not, you'll get taken advantage of. In the world of sales, he who cares most, loses.
