Charlie,
I know you don't want to change banks so the only options you have are:

1. Open a travel account with BankofAmerica and use ATM's fee free at (Santandar or Scotia bank ATM's). All others you will pay a fee.

2. Take the maximum amount out of the ATM you can per withdrawal so that you withdraw the least amount of times.

3. If you are there for a long time send down a Western Union money transfer to yourself right before you leave and pick it up with your Passport for ID. Depending on where you are staying you may or may not have a safe in your room where you can leave the money. You can compare your banks fees and exchange rates with WU to see which one would give you the best deal. If you have someone at home you can have them continue to send you money through WU while you are down there. If you open a BofA account ATM account for your travel, you can do "Safe Send" transfers online to pick up at Santandar or Scotia bank, fee free.

Other than that, if you don't want to use an ATM you are allowed to exchange up to $1500 per person per month, so depending on how long you will be there that may give you enough, just exchange at a bank or cambio. The first time you exchange you will have to fill out an information form and after that the information will be in the computer and you will only need to use your passport to exchange. You can augement this amount by purchasing something at a grocery store using US dollars and you will get change back iin pesos.