It's been a couple of years since I was on RCCL, but I think they were pretty much the same as others. Beer is roughly $6 to $8 depending on what you like to drink. But they usually have a special whereby you buy a bucket of 4 and get the 5th for free. Wine is roughly $8 to $12.
Figure about the same as a regular bar.
But don't forget, you can bring two bottles (750ml) of wine and/or champagne per stateroom onboard with you in your carry-on bags at the initial embarkation port only.
Travel Agent/Cruise Specialist w/13 yrs exp and 48 Cruises on 11 cruise lines! Favorites: Paul Gauguin - Tahiti: Uniworld River Cruises - Europe; Celebrity Solstice-class ships; Holland America - 12-nights Baltics & Russia; RCCL - 14-nights Greek Isles, Turkey, & Croatia; Holland America - 14-day Alaskan cruisetour; 10-night Canada/New England cruise; 21 days Hawaii w/7-night NCL cruise; Oceania - 25 days in Asia; more than 3 months touring Europe by train. And many all-inclusive resorts!