With all that said , buying your pesos here at a flat rate is still cheaper than yanking the $ out of an ATM in Mexico. I'm sticking with my previous statement.
Cheaper, I don't know, hard to believe it would be with a bank in the middle of the transaction. With my Schwab account I pay no fees so the only thing to consider is the exchange rate which all things being even should be the same But, even if cheaper, certainly not easier.