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.
__________________ 47 Cruises & Counting! Favorites: Paul Gauguin to Tahiti: Uniworld River Cruises in Europe; any of the Celebrity Solstice-class ships; Holland America for 12-nights in the Baltics & Russia; RCCL for 14-night Greek Isles, Turkey, & Croatia; Holland America for 14-day Alaska cruisetour; 10-night Canada/New England cruise; 21 days in Hawaii including a 7-night NCL cruise; Oceania for 25 days in Asia; & 3 months touring Europe by train. And many days spent in all-inclusive resorts!