A month or so ago someone asked about transportation from FLL to Port of Miami. I had made arrangements to use Super Shuttle/Airport Express and said I would let you all know how I made out.
I used a shared-ride van from FLL to the Port, $15. Very convenient, picked up van right outside baggage claim. The return trip had to be by private car -- $74 including all taxes and driver gratuity, all arranged ahead of time. This went very smoothly -- the driver contacted me by cell phone when he arrived and we met up with no trouble.
However, while waiting I discovered that Coach USA has shuttle service between FLL and the Port for $16 each way. No pre-booking required. Going to the Port of Miami from FLL, just go downstairs to baggage claim and find the bus (a small area -- very easy); on the return trip, just step outside of customs terminal and look to the right for the Coach USA podium.
On my next trip, this will be my mode of transfer from FLL to Miami.