I can't say I've attempted this yet but if you can wait a little bit I can probably offer some insight in a couple of weeks when we return from Jamaica.
We are flying into Kingston, renting a car and driving to Port Antonio for 3 nights before driving to negril for 6 nights then driving back to MoBay and returning from there. The cost of the car rental from Island Car Rentals is $300US for 10 days. My CC includes rental car insurance in Jamaica so I don't have to pay $14US/day for CDW coverage that I wouldn't otherwise be without.
I looked into taking the Knutsford Express (which we have used before and would recommend) but the schedule was very limiting to PA. Would arrive in Kingston at noon, have to make our way to the bus terminal and wait until 5:30pm departure to PA via Ochi and would have arrived at 9:30pm - a very long day of travelling. I'm not positive but think if you go MB -> PA you end up on the same bus out of Ochi. The return Knutsford bus out of PA leaves at 6am. I didn't want to have to set an alarm on vacation...
The Kingston->PA trip is ~100km and I figure will take this first time driver in Jamaica ~3 hrs. The trip from PA to Negril is ~300km and is 5 1/2hrs according to Google Maps. As it's basically another full day of travel in the midst of our vacation we are looking at this as an 'excursion' and an opportunity to see a part of Jamaica we haven't seen before (the PA->Ochi part). The road from Ochi to MB is excellent and a straightforward drive much like the highways at home. You can also download use google maps to download offline maps of Jamaica and put your phone in airplane mode and use the GPS functionality without requiring cellular/data.
I have read a lot online about the pros and cons of driving in Jamaica. It's not for everyone. After our last visit in 2014 I regretted we hadn't rented a car so I didn't give it a second thought for this trip. You can of course arrange private transfers to get you from place to place and not worry about driving but this would have cost much more and we wouldn't have the flexibility of a car in PA to get around to the various places we wanted to check out.
Hope that helps,
BS
