Keep in mind that the Cruise transport fee is per person. so $30 person is $120 (each way?) Whereas Dave's rate of $67 is per taxi. If you can get a minivan taxi, you might be able to get four people plus luggage in one taxi. Also if you have to be at the airport early on the return, the taxi is the less risky option. With the cruise transport they will wait until they have a full bus before leaving for the airport. So you could rush and push to be "first off" the ship, only to be waiting for 30 other people to get their luggage and through customs and outside...
Take the taxi.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013