The exchange rate used locally in Matzalan or Pueto Vallarta is usually 9 pesos to a dollar. The taxi drivers all take US dollars preferring these to pesos. Be sure to get a price the taxi driver before getting into the cab.
In Puerto Vallarta you usually can take a van into town, and these fares may be posted in US dollars. To get back to the ship you may have to take a taxi and do not be frightened if the taxi driver takes a different route back to the ship than the one you took into town.
In Matzalan stay away for the small open cabs that look like modified
golf carts. They drive like mad no matter what mode of conveyance you take but taking one of these carts is like "Mr. Toad's Wild Ride."
In Mexico try to use a can with as many other passengers-never alone especially if you are a female. If you buy anything expensive you may be better off using a credit card, if your credit card does not make an exchange rate surcharge..