I know Hickatee is correct, but I just thought I'd question the Belize Tourist Board about the departure fees shown on their website.
Here's their reply:
"The departure fee for departures by water taxi to Guatemala & Honduras is US$3.75, BZE$7.50. This is stated on our website."
I then sent a second inquiry, and got this reply from the same person:
"We confirmed with Boarder Management, who has informed us that foreigners spending more than or 24 hrs in the country pays a departure fee of $30 bze and pact fee of $7.50 bze. foreigners spending less than or 24 hrs in the country pays only departure fee of $30 bze. Should you require any additional information in this regard, you can contact Border Management at Tel: 823-3039."