Yes, for certain nationalities, it is free to enter Belize, but I don't think that was ever the question.
I just remembered that I have the link to the Border Management Agency:
http://www.bmabz.com/
And guess what! The information shown is opposite to the BTB information.
According to the Border Management Agency ...
"Foreigners less than 24 hrs (1 day): Pay ONLY Departure Fee (BZ$30.00).
Foreigners more than 24 hrs: Pay Departure and PACT Fees (BZ$37.50)"
DEPARTURE Fee is the fee charged to Foreigners once they are passing through or exiting Belize at the Belize Western Border or the Belize Northern Border less than twenty-four hours. The departure fee is BZ$30.00 or US$15.00. Foreigners should have a stamp that verifies that they have entered into the country legally.
"PACT Fee is charged to all Foreigners that have been in Belize for more than twenty-four hours. This fee goes to the Protected Areas Conservation Trust and is used help in the maintenance of the protected areas in Belize."
I think I'd trust the BMA site here, but I still hope you report on your actual experience, Maury. The BTB have been incorrect before.