We've stayed in the Blue Mountains of Jamaica (little known secret: the mountains are even better than the beach) and drank the coffee up there. If you like strong, rich coffee, it's hard to find better stuff than this. I should think that touristy gift shops are more likely to sell you fakes, unless it's an official Jamaica Tourist Bureau type facility. Coffee shops, just as in the states, are more prone to carry the real thing. Or even just stroll into a grocery store if you have the opportunity. That might be the best place to buy some.
I don't know of any coffee that's actually worth $20 a pound, but if you want to bring some back as gifts, it's always fun to hand someone a burlap sack with Blue Mountain coffee in it. Or better yet, drink it yourself and send them a postcard.
Safe travels,
cfurry