Are there any sunset "booze cruises"? Or just a tour around the island, maybe to see the lagoon? If so, anyone know the price range? I'm only gonna be there Dec. 5th and then going on to San Pedro. So it would help if I could plan this ahead of time.

Ras Creek, who has his boat at the split took us out one evening. I don't remember what it cost (not much though) but he covered much of the lagoon side of the island.
He has been there a long time and it is interesting to hear him talk about Caye Caulker

Ras Creek is the man to do what you are looking for. Can't miss him at the Split any day after 11:00am (if he wasn't out too late the night before)! Great guy, great staff, and a fun valued packed adventure! Highly recommend his experience.

Raggamuffin has a fun Sunset cruise too. We've done it a couple of times. I don't remember the price, but it's a good value for all the rum punch you can drink.

Thanks so much for the advice

I second the Raggamuffin recommendation. They took my whole wedding party out on a sunset sail - it was perfect.