This is our ‘go-to’ place when we port in Montego Bay. No need to purchase an excursion… simply we just take a taxi (~$7/person) to there. Great beach. Entrance is $6/adult ($3/child), and you can rent an umbrella/lounge chairs there. Food and drinks available for purchase. Taxi’s available to bring you back to the ship.
One advise: be firm with them with where you want to go, as they will try to make you go shopping and elsewhere for a “tour”. And don’t feel obligated to pay both ways when you’re going there as they’ll try to convince you to do that. Plenty of taxi to take you back when you’re ready.