We were at Costa Maya last December and went to the ruins at Kuhunlich. They are much better than Tulum. Covers a much bigger area with more buildings that you get to climb. With any luck you'll get the guide we had. He had maps, bird pictures that he had taken, plants and other items that the Mayans used that he passed around on the bus. Very good English and really cared about doing a good job and the history of the area. It was well worth the time and money. We did it as a ship excursion.
Even tho the tender ride at Belize is long, the boats they were using get you there in a hurry. Ours had 4 big outboards in perfect synch and the bow was riding high and you could have surfed on the wake. It was great.
All we did in Belize was go to the zoo.