Honeymooner,
They have a boat transport company in SP called Thunderbolt - real nice boats, I believe they go to Belize City. You should look into it.
The view from the plane ride is nice, but honestly, the times we went anywhere by boat was so nice and relaxing, we didn't get there fast but cruising by the mangroves, seeing the occasional dolphin jump, the horizon, and the spray of the water is all so nice, and I think maybe a better way to start your trip than boarding a MUGGY, HOT, tiny plane with eight other people. It would be a great way to start your trip.