I don't understand all the fuss about exchanging dollas to pesos.
If you keep in mind that a Peso is worth .07 U.S., you don't save very much if anything.
Most of the prices in Cancun are adjusted occasionally to keep pace with the exchange rate.
So it really doesn't matter if you get on the bus and pay 13 pesos or give him a U.S. dollar.
Dinners are the same way.
For example, take a $20 dinner;
The menu might be figured as 12 to 1 and you exchanged at 13 to 1. You will save less than .03 cents.
If you end up with extra Peso's at the end of your trip, you will sell them back for less than you bought them for making the exchange even less important.
I don't know, maybe I'm missing something.
If you could find goods with an exchange rate set long ago at 9-1 and could exchange at 14-1, it might make sense but those days are gone.