If you want to get the most out of your time in SP I would suggest taking a flight from Belize city or where ever is closest to where you are staying. I know it cheaper to fly out of the municipal airport than the international I believe it is about $75 RT compared to about $125.00, but don't quote me on that one!!! not to mention the extra time you will have to spend on the Island. By plane it takes 18 min, by ferry it is approx. an hour and 15 min each way. That to me is worth the extra money. Any way you chose enjoy La Isla Bonita