Here's a link: http://www.blackexecutivecars.com/index.html.
Quote $98 from Cape Liberty to JFK. See if they will quote for a city tour to kill time.
We did Caribbean from Port Liberty Christmas 2008. We had a limo pick us up from Port Liberty and drive us to all the sites we had missed in our few days before the cruise. Great driver who was very accommodating and knowledgeable, only downside for us was that the ship was VERY late back into port because of a medical emergency and our siteseeing was shortened. It was not expensive at all and the concierge on the ship gave us the recommendation for the company. We were then dropped at the airport for the appropriate check in.