Some of that depends on what and how much you like to eat. Here is basically what I figure per person:
Breakfast--we do cereal bars, poptarts or whatever in the room, so we don't budget anything for this. Easy counter service meal, I'd say $5.
Lunch--counter service $10 max and that should include a drink.
Snacks--need to have room in the budget for at least one drink, figure $2 and popcorn or ice cream $2.50 each day.
Dinner--this one depends on counter service or sit down. Sit down figure $20, counter service would be about the same as lunch.
Personally I think these are pretty generous figures. If you decide to do a character meal--yes, "grown ups" are allowed to go--do it at lunch time and it will be cheaper. There are much cheaper options for some meals too--like a baked potato in The Land at EPCOT or a turkey leg from the various carts. This should give you a general idea though. Are you familiar with the All Ears site? Check this out;
http://allearsnet.com/ She has all of the menus with prices on there so you can see what you would like and how much it will cost.
Have a great time! I travelled with my roommate on a cruise in college and it was one of the best vacations I ever had. And now the mom in me has to also say "Be careful!"