There is a trouble diagnosis tree in the 8D1 section of the FSM. That said, " after replacing the coil pack," makes me suspicious, the 14 pin connector with the single screw is notorious for not making good contact. I'd first try just pushing in hard at the ends. If comes back, remove the pad in the connector.
20,000$ seems high for that mileage. I bought a 1990 convertible for $7,000 with 65,000 miles on it. Perfect condition other than the AC needs work. He might be able to get $7,000-10,000$ but 20,000 is a real dream IMO.