Bus transportation here is a disaster. If you don't have a private car, use a taxi. JUTA (tel. 876/993-2684) runs a fleet of station wagons and minivans around the area. A typical charge, say from the heart of Port Antonio to San San Beach or the Blue Lagoon, is US$20 to US$25.
If you're being taken to the beach and want to spend some time there before returning, you can even arrange with a driver to be picked up at a certain time.
Minibuses operate throughout the town on erratic schedules and can be waved down. They are far cheaper, costing only US$2 per person. "Robot" or shared cabs are also plentiful, but some of these are illegal, and some of them aren't adequately insured. Know in advance that vehicles with red license plates are usually insured and authorized to carry paying passengers.
Note: This information was accurate when it was published, but can change without notice. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.