We went to Mayfield with Chicken, very reasonable and he's a hoot.

When we were there we were with a music festival doing shows in Negril. We invited our guides at Mayfield to come to Negril for the shows that night, free tickets. They said they'd love to but getting to Negril from there involved like 3 route taxi changes and they just didn't have the time to go and come back in the same night. So I'm guessing that taking route taxis there will be a bit of a pain.

With 8 people I doubt it would be any cheaper, either, as route taxis charge per person, charter drivers do not.