For my 7 night Greek Island cruise I pay around 1400 € for a inside cabin, including Free at sea, including gratuities, and including airfare Stockholm-Venice (return trip). For adding the Free at sea plus I pay 270 € more, also including gratuities. Totaling around 1700 €. I'm alone in the cabin so for two the price would have been way lower per person, obviously.
I plan to not spend any money at all on the ship, or max $100 for the entire week, I'll report back after cruise how it went.