Depending on which port facility you're traveling from, taxi fare will be between $9 and $10 each way, not including customary tip. Unless you've been here before I would NOT suggest you take the "dollar" buses. To even get to them entails quite a walk from either cruise ship port, they are hard to distinguish from regular taxis, they don't run on a regular schedule, they don't adhere to the taxicab commission rules, and their primary purpose is to supplement the government-run buses for locals who don't have their own transportation. Much simpler and way less time-consuming to take a regular taxi so you can really enjoy the few hours you have here. Have fun!