Red Stripe beer is never going to cost less than the economical USA brands that can be purchased for as little as 7 or 8 dollars a "12 pack" at groceries in the States.
It's good beer; on par with premium North America brands. I won't cost as much as Bud or Molson at home but it will be cheap enough.
Hard liquor (rum, local vodka) is the bargain in Jah; not beer.
It's actually difficult to find a whole 'case' of beer outside of the beer truck. You might have to hit the supermarket for a case.
Stripe is more commonly available in 6 or 12 packs. Figure on about a US buck a bottle in stores and 2 or 3 dollars at a bar.