Welcome to the forum! There aren't many all inclusive resorts on the cliffs of Negril - Samsara is smaller and not as fancy, and The Caves is very fancy and beautiful but more expensive.
I attended a destination wedding at Sandals Negril earlier in the year on the beach in Negril, and they had the ceremony in the gazebo by the beach. The beach and ocean were right there, but the aisle was a sidewalk and surrounded by grass. They had a small reception on the lawn next to the gazebo and dinner later in one of the restaurants. So, you don't necessarily have to get your dress all sandy - many girls mention having their ceremony or reception on a pool deck overlooking the ocean, so that is another option as well. The cliffs would be beautiful though.