Industry Rate
We get a crew discount @ Marriott in Grand Cayman, but airfare from the states runs in the 400+ range, unless you can JS (American, USAir, Continental go there) Rate with the crew discount for a standard room is still 180 US. Temp right now is in the 75-80 F range.
A few months ago, we stayed at the Westin Lucayan Resort in Grand Bahama. They gave us a pretty decent discount (140 per night). I think they are about 70 F this time of year. Someone told me there is a high-speed ferry that runs from Ft. Lauderdale for about 100 per person.
A little tip, most hotels will give crews what they call the "industry rate". Most of the time they won't ask for ID, but have it ready. High end hotels and resorts often have blackout dates for their discounts during peak season (right now in the caribbean). Call and ask them to fax you a rate schedule, then plan your vacation accordingly. A few days can make a huge difference. Be sure to ask for the "industry discount", as the front desk personnel may not know what a "crew rate" is.
Have a great time.