We did the Land and Sea excursion...excellent land tour of all the island highlights (Pitons, Soufriere, Sulfur Springs/volcano, Botanical gardens) complete with lunch; followed by a gorgeous catamaran sail. We stopped for a swim @ Anse Cochon, sailed in and out of Marigot Bay.
We got a cab at the ship dock. Driver's name was "Doobie" Paid him $40 for 4 people and he rode us around stopping everywhere for 5 hours. He was very knowledgable and informative. We went to the pitons, saw the volcano where he had some local guy carve a face in wood for me. We stopped a man riding a bicycle and paid him $1 to climb a tree and get us a coconut, open it and let us taste it (I gave him $5). Everyone was willing to do whatever we wanted, cheap. Of course we paid a few more than their asking price. We stopped along the rode and looked at plants and flowers. It was one of the best excursions ever.
Can't be sure you'd get such a great cabbie but ask around to see if he's still driving.
We took a ships excursion by boat to snorkel at the Pitons--it was great! The trip to the location was as much fun as the snorkeing & to swim in view of the Pitons is awesome! We didn't get to see much on the land but did not want any long drives on curvy roads. Our guides were great!