Personally, I would find out if the place I was going to be staying in both Ochi and Negril had a driver associated with their property and, if the price is reasonable, negotiate with that driver to include your day trip needs as well. Money talks so spending it with one driver in each location should get you the best deal. Getting a Negril driver to service your Ochi needs (or visa versa) will not be cost effective. A secondary choice might be JUTA or Knutsford Express Bus.