rastagal - I have used Island Rental a few times now and taken advantage of their service of delivering it to me in Negril. I think it was $20 first trip, I think $30 last time, but not positive.
If you're wondering why I didn't just get the car at MoBay airport and avoid the delivery fee - I just use route taxis for 1st week unwinding and don't need the rental car. 2nd week is when we take day trips and need the rental. I use the rental car to get back to airport at end of trip, avoiding that delivery/pickup fee - plus I save the taxi fare to airport.

When I did it, Island's weekly rate, even adding in the delivery fee, was cheaper than anything I found locally in Negril. Plus I liked that they have 24hr road service anywhere on the island. But that was about 9 months ago - in low season.
NOTE: I have one of the few Credit Cards that DOES cover the Insurance in JA - most do not. Search these threads for more on that topic if need it. That could change cost comparisons if you do not.