Grant, No flights between Chetumal and Belize that I know of now, I'll check some sources. There are 2 flights a day between Cancun and Chetumal and return, I don't know if they operate 7 days a week, maybe someone else will have that answer.
Taking taxis to cross the border is good, the driver may be able to help you speed things up, the problem is reentering Mexico in the afternoons, there is a free trade zone just inside Belize and a large number from Mexico do shopping there on week-ends. We have been told the wait is up to 3 hours, buses, trucks and cars, it's a 2 lane bridge, 1 each direction.
Grant, do a search in Yahoo for "getting to Belize" see if you can find a forum there to help you......
If you can get in to Chetumal early, you can get your ticket for the next day, you can buy you tickets either at the bus station downtown, near the museum. For a hotel in Chetumal, I would try the Real Azetca, also near the Museum.
What time is your flight out of Cancun? If it's not too late, you can stop in Playa and get a bus to the Airport for $7/US each.
[This message has been edited by Su_Amigo (edited 01-10-2002).]