All items sold in Mexico are priced in pesos. The current exchange rate is 9.3-9.5 pesos per dollar at the banks and fluctuates daily. For the best exchange rate, use your ATM card at the bank and pay for your purchases with a credit card. They accept cash and traveler's checks. The stores, bars and restaurants will often exchange money but at an even lower rate.
Hotels give the worst rates.
Be sure to count your pesos whenever changing money. Exchange rates are usually clearly posted, but if not, ask beforehand. A letter to the States or Canada costs four pesos and may take 7-14 days, a post card longer, as all international mail goes first to Mexico City. If you buy anything bulky, ask at the store about shipping. There are somewhere around a thousand taxis in Puerto Vallarta.