If anybody needs a reliable and affordable private transfer from Belize to Chetumal, I would recommend Delphin Swasey. He is a very honest man, who is fluent in Spanish and English. He lives in Corozal, Belize.
My wife and I used Delphin's services, he took us to Cerros, and the Smuggler's Den in Consejo, as well as into Mexico.
Here is Delphin's contact information:
He is usually at the Corozal Town pier every time the Thunderbolt comes from San Pedro.