Yep, that was from me. As of October 9th give or take a day the fee doubled to $40 per person. We were told this at the cab station in Jamaica and confirmed it with the local port authorities. Their story is that the ownership of the Sunset Beach resort has changed.
Even though it has gone up in price, you still may want to consider it. First of all, it is guarded to keep the locals out. Jamaica is a very poor country and the locals will hound you to death trying to sell drugs, braid your hair, etc.
Second, we went to Doctor's Cave beach and were nickel and dimed to death. $5 each to get in. Great fee, but small beach front. $5 for each (rickety) beach chair rental. $5 for an unbrella rental. You pay for your own drinks. You pay for your own food. We ate and drank down the street at Margaritaville, and after all was said and done we were out $75. And we only spent about two hours on the beach. If we had stayed all day, it would have cost us much more in drinks alone.