It all depends on the length of the cruise, month of sailing, type of room and the destination.
I looked at the
Disney Cruise Line site, ran the numbers for all 2018 cruises. I did the cost for 2 adults, 0 children in one stateroom.
The cheapest options are as follows:
Alaska $3459(7 day) to $6683(9 day)
Bahamas $1393(3 day) to $4184(7 day)
Bermuda $2561(5 day) to $3239(6 day)
California Cruise $1386(4 day) to $2397(5 day)
Canada and New England $1905(4 day) to $3580(7 day)
Caribbean $1676(4 day) to $8467(11 day)
Europe $3231(5 day) to $7618(11 day)
Mexico $1216(2 day) to $3366(7 day)
Panama Canal $4746(14 day)
Transatlantic $3758(11 day) to $4597(13 day)
The average across the board is: $2563(low end) to $4887(high end)
True average would be: $3725