I can't argue with the convenience of laying in a supply at your local bank. There is a cost to this. In Bill's example above, the rate was 20.20 pesos/USD vs. whatever the official exchange rate was on the day of the transaction. But for the OP- who started this ball rolling- this is for a first trip to Mexico. They are not going to know how much to exchange. For many of us who travel regularly, having a little 'carry-over' local currency- Pesos, or Euros, to take care of 1st day expenses until we get to our preferred exchange place is great. But for those on a first trip- who may never go back- the odds of having foreign currency that feel 'forced' to spend before leaving (I have some Saki from Japan just because of this) increases the cost far above an ATM fee.