At the Banamex ATM in Sam's, I received 20.7 pesos on Thursday when the peso was trading around 21.3.
The Peso was trading erratically as was the whole currency and stock markets as the DOW was down 2000 that day.
Peso is at 21.9 today (Sat).
The Banamex ATM's have always given me a exchange rate close to what the currency markets were trading at.
The Elektra store will allow you to wire $$ for pick up later, also Western Union. Fee's ?