In Ocho Rios the "Taj Mahal" market isn't too bad of a place to try. It's close to the cruise ship pier and has a variety of stores including jewelry. Nine years ago I bought a Breitling watch there and it was the best price I have found anywhere. It's also a great watch (it better be since it's a Breitling). I wear it everyday.
Grand Cayman isn't the "Bargain Capital" of the Caribbean. The jewelry stores will charge you about the same and sometimes more than you can purchase things in the states. However, their quality is first rate. Each time I'm in Grand Cayman I, at least, wander over to Kirk's Jewelers and check out the watches. The pier area has some shops where you can buy t-shirts, rum cakes and other touristy stuff.