Miami Airport straight to the Port of Miami or vice versa falls under the "Flat fares" and is $24. They may have added a fuel surcharge. Flat fares are posted on the rear seat passenger window. No taxi driver should be charging more than what is posted. Some have tried to charge passengers the port fee they pay when leaving the Port of Miami. Do not pay it. If they try to charge you, point to the sign and remind them all fees are included. I make it a habit to write down the taxi number and driver number when I enter a cab.