Maralunatic,

Great idea to visit the south coast. Others can provide pricing.

The itinerary that I use is as follows:

Leave Negril after an early breakfast. Black River Safari ( I recommend a smaller boat, there is a bridge across the river upstream and larger boats have to turn around at that point.
Pelican Bar is optional if you have time and the funds.
Drive through Bamboo Avenue
Stop at Howie's for lunch
Visit YS Falls for an afternoon dip
Stop at Appleton Estates for the tour and a few samples
On the way home stop near Bluefields Beach for some Spicy Shrimp purchased from a roadside vendor.
That is a full day of fun.