We took our own self guided walking tour. We weren't sure what to do since we didn't get into port until 3:00 p.m. I found the idea just by searching on-line. We followed the map and visited the large historical fort that surrounds the port. A tour of the fort was only 3.00 per person. Stop in the information center where the tour begins and get your free rum drink.
We took a cab to Maho Beach (aka Airport Beach) and spent the day watching the planes land and take off. We visited Airport Beach last year as part of a tour and wanted to go back since we didn't get to spend as much time there as we would like to. A cab ride was 8.00 per person each way(it's more if there are fewer people).
Took about a one hr ferry ride to St. Johns. The ride over was very rough (take something for sea sickness if you are sensitive to motion). Once we got there, I was ready to get off of the ferry. We had to remain on the boat if we were taking a tour of the island by boat. The actual tour was fairly short, but the ride was calm this time. They showed us a view of numerous beaches. We then got off of the ferry boat and took cab to Trunk Bay (the visit to Trunk bay was not actually a part of the excursion). There was a cab charge of about 6.00 per person each way and a 4.00 per person charge for the beach. If we would have known, we probably could have just purchased a ferry ride to St. John's and then took a cab to the beach for less $.