Here are a few unexpected higher costs for your cruise.
1st - A ship transfer cost from the port to FLL is $15-$20 pp. A cab cost ~$15 for the ride. Cab goes directly to your airline, shuttle goes to everyones airline before yours.
2nd - Book your cruise then look for good airfare to & from FLL. You may be able to get a good airfare to FLL, but if your ship returns on a Saturday or Sunday be prepared to pay 50% or more for a flight home after 10:00am until 6:00pm. There will be 7 or 8 other ships (incl RCL's monsters) arriving and the airlines know that. To get around that, if you live w/i a days drive and it is a winter cruise, rent a car and drive it. The car rental agencies have an excess of cars in Florida and will charge a very norminal drop off fee.
I used Fort Lauderdale as an example, but other ports may be the similar.