St. Thomas: Rum was about $8 a bottle; Tequila about $13.
Alaska: On board was a special for liquors at 2/$20.
Hope this helps...
Oh, BTW, if you plan to go to the rum plantation, don't. Ask a local cab driver to take you to the plantation that the locals go to. Best rum in the world.
check the prices out on board first. If you see it cheaper in the ports Starboard (carnival, celebrity, rccl, holland america) will match the price for you. I've worked on 2 contracts in the gift shops on carnival and the only thing i have ever seen cheaper is sometimes particular tequilas in mexico, or tequilla from cabo wabo which the ship doesnt stock.
Trust me you've got nothing to lose by checking the prices out on the ship first.