My cruise account for a 7-Day cruise averages $400 to $450.
The biggest charges were for the shore excursions which I book at the desk onboard during the cruise. I know you might be able to save some by booking in advance, but I feel better waiting until I get onboard.
Also, I spent allot of time at the Internet Cafe onboard, emailing my family and friends. I am sure that was a big charge on my onboard cruise account.