I know the Carnival transfer rates from FLL to Miami Port are $32 return, and you can purchase them one-way for $16.
Can you get a taxi (van?) for six people?
Otherwise are there van/limo shuttle services available other than a coach? The only reason I ask, is that I was wondering if having a limo/van waiting for you would be quicker than waiting for a bus to fill up?
We have reserved a "meet and greet" Towncar for $68.00 (incl. tip) from one of the local Miami transport companies for the four of us from FLL to Miami. I understand this particular company also has plenty of vans available for share rides. You can E-mail for the company and contact information.