Cyndi - I found the following for you:
http://www.miamidade.gov/portofmiami/directions_parking.asp
Directions & Parking
Directions From I-95:
Take I-95 north or south to I-395. Follow the directional signs to the Biscayne Boulevard exit. When you get to Biscayne Blvd., make a right. Go to 5th Street which converts to Port Blvd. (landmark: American Airlines Basketball Arena) make a left and go over the Port bridge. Follow directional signs to designated terminal.
Port of Miami
1015 N America Way
Miami, Fl 33132
Port's Map
Parking:
Parking is available in facilities located in front of individual cruise terminals. No reservations are required to park at the Port of Miami.
Long-term parking for a regular vehicle occupying a single space is $20 per day. Short term parking is $7.00 if you are coming to see someone off but, not intended for overnight parking. All Cruises in the current itineraries would fall under Long Term Parking.
Rates will vary for larger vehicles (ie., oversized vans, recreational vehicles and vehicles with trailers). If the vehicle is over 20’ in length then an additional $20.00 is added per day. Therefore, these larger (ie., oversized vans, recreational vehicles and vehicles with trailers) cost $40.00 per day and all oversized vehicles can only park in Lot #2.
Currently garages C, G, J, and Lot # 2 accept either cash, credit (Visa, MasterCard, American Express only), or any major U.S. Travelers check.