There will be shuttles lined up at the port. You can also walk out to the main street and take a taxi. Yes, the shuttle will be priced as a one way pp. Taxi will be a flat rate but ask what the rate is before you get in. We've usually paid approx $10.00. for the two of us one way for a taxi. When you're ready to return go one block over from the Malecon (one way traffic) and flag down a taxi (easy to do) tell them back to the port and again price before you get in.
We pay in USD for the small purchases we do in port, for us not worth getting pesos, but it's a personal choice.