To add to what Tom has already told you, here are my suggestions:
First, returning to the airport using Disney's free service is probably the best option. Most shuttle services to the Port are provided from the airport. You can use the cruise lines transfers, but depending on how many are in your party - it may be more economical and convenient to reserve transfers from an independent company. I know Majestic Transport offers service for $80 one way (http://www.majestictransport.net
). A taxi will cost well over $100. The port is about 50 minutes to an hour away from the airport. Another option would be to rent a car (one way). Florida is probably one of the best states for offering very reasonable one-way rental rates. You can drop the car off at the rental car company and they will transport you to the port.
Now, after the cruise: You might again want to consider renting a car. This way you can spend the day at your leisure visiting the Kennedy Space Center and then head back to Orlando for the remainder of your trip.
As for Captain Marvins, Here is the website:
Hope this helps-