There really is no "realistic" budget. There are just too many variables. They joke about the people who can't have their ship account slipped under their door on the last night because it it too thick....but that can happen. On the other hand, you can have a great time on a relatively small amount per person.
First...do you need/want internet ($89)
Do you need/want soda/beer packages? You have to drink a lot of soda to make good on this one!
Plan on $80 per person for tips (7 day) to meet the minimum recommended
Shore excursions...booking thru Disney is the easiest, but also the most expensive. You can look at the available excursions and prices on the
DCL website or Barb's site
www.castawayclub.com
Photos--these can really add up in the photo shop. On the other hand, the DCL personnel will take a picture with your camera at the same time the ship's photographer is snapping the professional shot. You can spend a very lot or a relatively little.
Arcade cards...this is an item that I make DD pay for if she thinks she needs one. There are plenty of other things to do on the ship!
Alcohol....again, you can spend nothing or the sky's the limit
Drinks are about $4- $6 each...free at captain's reception,
castaway club reception, and the cooking demos!
Shopping/souveniers...again...you can stick to YOUR budget.
Spa? Unlimited Rainforest is $50 (7D) See Barb's site for rates for individual services. Again, you could drop $1K per adult in the spa or nothing at all...or anywhere in between.
Palo's ....relatively small amount, but adds up....
You can EASILY spend $1000 per person if you do the most expensive everything....or have a great time on far less than that. It really is a matter of your taste and choices. Will you really miss not having internet for a week? That might make internet a necessity rather than a $89 luxury. There are places on shore that you can have internet access for $1 for 30 minutes. WOuld you rather spend your shore time on line? What is it worth to you.
It's sort of like asking what is a reasonable budget for WDW. Do you plan to stay at the Grand Floridian or the All Star? However, on board, there is far less difference between the highest and lowest spenders.