tbserena: Others may disagree, I am not if you are going to get an average cost/spend for a cruise.
I am not sure if you have lrking on these boards, so I will attempt to list items that you may want to consider that will cost you on the cruise:
Crusie: Depends if there are 5 or 4 in your family. If there is 5 you are looking at a min of two rooms or a cat that can sleep five and depending on the time of the year it can cost more than two rooms. (Cost depends on cat and time of year)
Transport: If you are looking at transport from the airport to the port, limo (Cost 160 - 200) or car rental (Cost is 30 -60) is the cost effective way to go.
If you drive, parking is 10 dollars per day??
Tips for porters, room attendents, head waiter, waiter, asst waiter.
Other than the cost above which is somewhat out of you control other cost on the ship that you can control:
Arcade games
Picture package
Soda package (only in dining rooms can you get soda as part of your package)
Wine
Drinks (smoothies and tropical drinks)
Excursions
Spa
Special coffee
Shopping on the ship and on shore
We did not go overboard, but we got a picutre package, some wine, a spa, a couple of smoothies and an excursion and I recall the cost being close to 800 (cruise, travel, transport, night before cruise hotel and tips not included)
Hope this helps you.