Since you are going to be in the vicinity of Ohio/Pennsylvania, I would definitely make a stop at Knoebels and Waldameer Park. Both have free admission and pay-per-ride systems. They are great small parks with only a few coasters, but they are some of the best world-class coasters in the states. It could be only an hour or two visit at each park and wouldn't waste a day of your trip-you may even drive past them on your route.