It was cancelled about an hour after we arrived so I only saw it from the ship but we've been there before and it's a great day for lounging at the beach!
Take a cab (not the ship excursion) to Sapphire Beach. It was just 10 dollars per person each way and the lounge chairs are just 7 per person. In total it comes to about half of the ship price. A great day!
We just took the boat to the main town and did some shopping. It was convenient but very hot. Hagglers in the shops weren't too bad.