From FLL to Miami is best , IMO, rent a car. That is most economical way to go. Your driving time should not be over 1 hour 15 min. Most Rental agency there have shuttle to the pier. Check them out.
. 7 days-Cruising on Carnival Magic Dec 3,2016--7 days from Port Caniveral--Cruising on Carnival Vista, 8 days, Jan 27, 2018 From Miami, FL.Cruising on Carnival Valor 5 days from Port Canaveral Feb 22,2018
A rental car, as Ray suggested, is not a bad idea. BUT.. rent from an agency with a drop off point at a hotel in the pier area. Otherwise, you have to return to the airport, and shuttle back. Not that difficult, just time consuming.
I know Enterprise has a location about 5 minutes from the Miami pier, and I believe Budget is located in the Biscaynne Hyatt.
They won't let you turn in a car at the Hyatt. That's why Jose and I always rent from Enterprise and turn it in downtown on Biscayne Blvd (Hotel Dupont??) then take their free shuttle to the pier.
Thanks for the info I knew you all would know what to do. 6 of my family are flying in at the same time to Fll and we can't fit them all in the car,,so they'll have to make arrangements to get to the ship.