According to the Port of New Orleans web site, it is $70 per week, exact change or credit cards required.. Your friend might have parked at a private lot nearby and paid less.
My sister just left out of this port on Sunday (11/18/01) and it was $70.00 for her to park. You can check out the web site. It is www.portno.com They have a web cam that you can see the ships dock (Inspiration on Sundays) and on Fridays another Carnival ship is in port. Can't remember the name but it's neat to view the pier and dream. Also to count the days till you will be there!