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I went on the Sea Princess last year and the wine was about $28 for a cheap bottle, plus of course 15% added onto to every purchase. Sorry I cannot help with the beer.
All prices in USD and approximate. Beer (bottles/cans) 3.50 - 5.25. Cocktails 4.25 - 6.50. Scotch 3.95 - 9.50. Gin 3.95 - 9.50. Plus, as Carey says, 15%. Hope this gives you some idea.