I did that exact same cruise in December 07. After a couple of days on board I got a complimentary ticket for a transfer back to JFK, which also included a mini tour of New York. My flight was at 18.00hrs on the day we disembarked. I think it all depends if you have your flights booked through Cunard or not - I did. If you have not, then there is an option once on board to book a transfer (there were ones that went straight back to the airports, others which had a longer tour of New York), all depends when you need to be back at the airport. Sorry not sure on the cost though. Hope that helps.