Exchange rate and prices of pesos and USD.
As of right now, the current exchange rate is 12.5 or 13 pesos = 1 USD. That is what you will get at the bank/money exchange.
The exchange rate that taxis, shops, and restaurants use is up to them. The taxis in general are giving the tourists $10 pesos = $ 1 USD. That is 25% lower. So, you will need to get pesos ahead of time to pay the taxis.