Find the camera you want before you go and gather prices in the US - then price is down there. That is the only way you will know if you are getting a good deal. My husband is a photographer and has always priced in the Caribbean and has never found a better price then here in the states but then again, you never know when you'll find a bargin. But, the way to find a bargin is to know what you're shopping for and how much it costs in the states.
Purchased a digital camera on board ship pricin was same as in states and in saint thomas I used the camera from the first sea day through the last day the camera guy helped me learn to use the camera and gave over 50 pictures at no cost
Western Caribbean are not usually the great shopping locations that the Eastern offers .
One of the best places in the US to by a camera is B&H Photo in New York. They have a catalog, a web site and of course the store. Get the price of what you want to buy from someplace like B&H and you will have a great starting point of reference . Royal Caribbean (no relation to the cruise line) in St Thomas is reputed to have very good camera prices. They may sell on the web as well. Your typical Western stops of Jamaica, Grand Cayman and Cozumel are not necessarily noted to be great shopping meccas. Good luck.
Camera equipment available in foreign ports are called gray market, ie, they do not have official US warranties from the manufacturer. Repairs or service can be difficult. Watch the wording carefully. Some say US warranty but it is not from the manufacturer but a third party. Watching the pricing thru amazon or internet through reputable new product stores is best way to know price, and then watch for specials, like a lower price, $50 gift card thrown in or bag or extra memory card etc to give you lower net price.