Most have the prices for 3 hours and what type of room written outside on the wall, Avg RD400 ($8) for basic room. The Isla Paraiso (sp?) is the only cabana on the left as you are leaving POP that I prefer. It's about a mile after the University and Zona Franca. If both of you can't speak Spanish, you can tell the operator there in english when the phone rings for how long, and any drinks you may want. You will receive a bill in a spinning door and you will need to pay 1st before you know what.....lol
Getting there depends where you are coming from. If you are in the city or just outside it, then I would go to main carrito station and offer an empty car rd200 and tell him to take you two inside the cabana you choose. After you are finished, you can take a carrito along the highway which is right outside the gate heading into POP, or arrange with the driver his contact info and he maybe able to pick you two up.
If your going to a cabana with a local, making any arrangements should not be a problem, it really depends on where you are coming from.