Sending by regular mail will take a month or more to reach Belize, (verified by experience). You can send by courier (DHL) but the bank here will probaby put a hold on the MO for a week or so. Yes, the banks do charge a small fortune to wire money here.
Western Union is the best for sending quick emergency cash, but if you are going to send money to a friend or relative on a regular basis, I find that it is best to send the reciever an ATM card and then just deposit money into the account back home.
don't know your situation, but if you are sending money to a poor little Spanish/Belizian girl you met down here, or an undeveloped resort property STOP! you are probably getting suckered.