This site has a lot of navigators. Read the most recent dated ones and it will talk about some pricing of drinks.
Disney Cruise Line Navigators
Hope this helps both of you.
If you have more questions please ask, I am happy to help when I can.
Feel free to contact me through the PM section of this thread if you want.
We just booked our 21st DCL cruise for 2011, so I do have some experience with them. Happy tp help!