Chica, Which dive shop often depends on where on the island your staying. We have a lot of good ones spread out over 15 miles or so and transportation is an issue on Ambergris as you already know.
You should try and do the New/Old North Turneffe Trip. Amigos del Mar has started doing it again after years of not visiting it because of the severe Hurricane Keith hit. It's come back strong, the fish and corals are amazing again.
North Turneffe Atoll 165.usd no park fee.
This extraordinary dive trip visits three sites on the North point of the
Turneffe Atoll. It offers spectacular diving and pleasant sea conditions, making it suitable for divers of all levels. Divers experience calm seas and a steady boat, as the atoll protects sites from weather.
The atoll stretches 30 miles long and 10 miles wide, is undeveloped, and protected by Belizean law. Visibility is excellent, ranging from 100 to 150 ft., making it easy to enjoy large pelagics, rays, turtles, eels and schools of snapper, horse-eye jack, and permit. Because of its isolation from development, coral life flourisheds.
Its also a good bad weather choice. In other words when it too rough to dive here on Ambergris Amigos has a route inside the protection of the reef and in the lea of the atoll that can get you there and when your inside The Turneffe Atoll its always like a lake.
Amigos has a large boat especially nice for the trip since you'll be spending all day on a boat that's important.It leaves at 5:30 am, they pick up at your hotel dock and brings you back 5:pm ish.