Just like a land based vacation...that's really up to you. Pictures run, $20-25.00@, drinks are $4.00 to 6.50@. Don't forget the tips if they are not part of the original ticket price. I hold $20.00 per day for two people for tips.
Gambling, bingo, shore excursions and ???
I have seen people 2 spend $750.00 and others that spent as little as $50.00
Hope this is a little help.