There is a Belize Bank with an ATM that accepts most foreign cards, and also a branch of Scotia Bank. The bank will only let you buy US$50 and charge a US$2.50 service fee. You can change your Belize Dollars for Guatemala Quetzales with moneychangers infront of the immigration office and at some hotels at a rate of Q3.5 for BLZ 1a 10% loss.