According to information published by this website, prices for Royal Caribbean ships including The Independance of the Seas are, $5.00 (£2.50) for a glass of wine, $4.75 (£2.50) spirits, and $4.00 (£2.00) for a bottle of beer. I don't know how up to date this is though? Happy cruising.
There is no prices to search for on the web but a bottle of beer is $3.50 so about the same as the other ships 1 gin/tonic would be around $6.50, but they usually are bigger measures than back home.
Here is a link to the prices for froo-froo drinks: http://travel.webshots.com/album/559018541CiiBCu?vhost=travel and here is the link to the wine prices: http://community.webshots.com/album/562747533yjShXM.
The prices are on a par with nicer pubs.