If you're looking for something similar to what you get in the airport...the best price for coffee in Negril is going to be the grocery store HiLo or Value Master or in the West End, L&M.
Rum cream is more affordable at Quality Traders over HiLo. But, they don't package it as nicely as they do in the airport....though you can ask for extra paper to wrap up your bottle.
And, remember you have to put the rum cream in your checked luggage...it can't be carried onto your flight.