Thats about the going rate for parking in and around NYC. I've just paid it the two times I've cruised out of NY. Park & Cruise rates might exist at some hotels across the river in New Jersey but then you are adding on the hotel plus transportation to the port. Not sure you come out that much ahead (unless you were coming in the night before anyways).

The Hilton at Penn Station in Newark offers easy transportation, but still charges 21$ a night for parking. I don't remember if they had park and cruise rates when I was there last week.