Belize is not a cheap country, so bring as much as you'd need at home if you were travelling & eating out, etc. Allow plenty for trips you might want to go on. Try to bring all you'll need in US$ cash and US$ travellers cheques. Most businesses won't take American Express, because Amex give them such a poor deal here - bring Visa/Master. But try to keep the credit cards as back-up - any credit card is costly for the business concerned, greatly more so than at home; though some don't charge extra, many do.