I believe the cost of the valet parking as of last summer was around $15 or $17. You should of course tip the staff. We did this last summer. It was indeed convenient, though poorly thought out. We had an early breakfast, then stayed all day at the park, and attended the Halloween party afterwards. By the time the day was over, we were pretty tired / exhausted. It was a LONG walk back to the car, even though it isn't really all that far.