there are many hired cars available in Jamaica, and OR to MoBay is about an hour IIRC. I'd be surprised if any good hotel in MoBay couldn't put you in touch with one, or even arrange it for you. That being said, I would not rent a car and drive myself on a bet in Jamaica - the roads are quite narrow, if you are not used to RHD and left side of the road, with fast and crazy drivers (and goats, and chickens, and...) - I usually grit my teeth when riding there