The website for JFK is
http://www.panynj.gov/airports/jfk.html. Click on "Ground Transportation” it will give you all the transport options.
While the above routing suggested is certainly cheap, it will take several hours. In addition to the time, I myself would not want to do that many transfers, deal with buying that many tickets, and would not want to lug bags onto the PATH or worse the subway (stairs are likely to be involved on the subway). Also if your journey is during rush hours, the PATH and subways are likely to be very crowded with commuters will may not welcome you and your bags.
The next best in terms of cost/convenience would be the direct private bus service between the two airports. It takes 90 minutes and costs US $30. Runs every hour on the hour. Take a look at
http://www.olympicairporter.com/services.html or call Airporter at 1- 732-938-6666. You can reserve a seat ahead of time. See
http://www.panynj.gov/airports/jfk-a...nnections.html for other direct bus options.
You can take a private car service for a faster trip. Something like Dial 7 car service will cost about US$80-100 for the transfer, depending on the car you choose and number of bags. The rates do not include tolls or tip. You can simply call them when you land, or make an advance booking, see
http://www.dial7.com/. (Calling when you land is easier as you won’t be charged wait time, they have lots of cars standing by.) Without traffic the trip between the two airports will take about an hour. Rush hours are weekdays and are generally between 7-9:30 am and 3 – 7 pm, and can add to the overall trip time.
A cab is also possible and would cost about $80. See the website for JFK airport listed above for info.
You say you have plenty of time, I would think that as a comfortable cushion you would want 4-5 hours between flights just in case all things go wrong like lots of traffic, some security issue on a bridge or tunnel, etc.