Ahoy, Carolan!
In my experience, I find it much more cost-efficient to purchase wine by the bottle on a Disney Cruise. If you order a bottle and don't finish it in one sitting, your servers will be more than happy to re-cork it and store it for your next meal. You also have the option to take it with you to your stateroom to enjoy.
If you plan on enjoying wine each night, Disney Cruise Line offers a wine package that can help you save up to 25%. With a wine package, you'll receive a bottle of wine for each night of your sailing, chosen from an extensive wine list. At the end of the cruise, unopened bottles can be taken off the ship with you (remember to claim them on your customs form).
You can check out the wine packages offered on the Disney Cruise Line
Gifts and Amenities page, in the Food and Beverage section.
I hope this helps with your planning! - Diane W.