Thinking about a "Test Drive"

There's a shuttle from the airport to Placencia. There's also Maya air and tropic air. There are also buses, although they aren't super comfy, other than the express buses, which are quite nice. As for local travel, the buses and taxis are fine while you decide if you want to stay.

The choices are private mini busses usually associated with the more exclusive hotels,  very pricey sometimes subsidized by hotels. next  are mini busses from the areas privately run some associated with tour organizations still quite pricey need to have someone book seats in advance for you on mini busses. Then there are the local air companies with fast pricey puddle jumper flights.Not cheap but very convenient again need to book ahead. Then there are expensive  private taxis down to Placencia. there are usually taxis  as you leave the airport. It  is a 2&1/2  hour or longer drive from the airport in a private vehicle or bus, Fuel is expensive and you are paying for the drivers time to get there and he has to get back (the hotel/private busses will probably have brought in passengers flying out earlier) the other alternative is either rent a car and drive yourself,  Auto Rental offices as you come out of the door at the,  airport or use local busses. The local busses pass the end of the Airport Drive, About 1 and a 1/2 miles from airport exit, catch a bus to Belize city or Belmopan and change to the Placencia bus at the main bus station. This is by far the cheapest route but can take anything up to 6 hours including change time. the local busses are OLD american school busses repainted in one of the many bus company liveries. Possibly not the best introduction to the country unless you like uncooled school bus transport with often very loud rap type music on a loop for that 6 hours.
A few years ago we took a Taxi  from the Airport to the main bus station in Belize city  and then a bus down to Placencia  we met several people to chat to on the bus and it was actually not as bad as this my description sounds like it would be. We were meeting friends in Placencia who had a car to loan us for the rest of our vacation.

The express buses have AC. They don't go into Placencia, though. You'd have to take it to mango then catch a taxi to the waterfront and then take the hokey pokey water taxi over to Placencia. Not as complicated as it sounds.