Jamaica's water (among other things) is down right dirty compared to Cayman. While Cayman is one of the (if not the) most expensive places in the Caribbean, it is worth every penny and dollar plus some.
Great water, great reefs, great people, fabulous diving, they speak English, there is no crime, and you can drink the water. Lunch for two at Burger King will blow a $20 bill, but the Wendy's is still reasonable. Plan on $100 (or more) for an average dinner for two. Chef Tell's is a waste of money, but there are lots of great places to eat. Conch fritters on the patio at Sunset House (at sunset of course) with a Rum Punch is what life was meant to be about.
I got my initial scuba certification in Jamaica (took the written sitting at the bar sipping a Red Stripe), but it pales next to Cayman.
There is no place like Stingray City. You, the squid in your hand, and 10-30 stingrays swimming all around you is just about as good as it gets.
Nuff for now.....