Last year when I was planning my cruise on the
Carnival Triumph, I was planning to drive down to Miami and park my car in the parking garage there on Dodge Island (Port of Miami). However I found out that they raised the parking rate from $12 per night to
$20 PER NIGHT! 
. That was totally unacceptable.
Then one of my supervisors at my job suggested that I do a one-way car rental twice. I would rent a car one way from Orlando to Miami. When I dropped the car off in Miami, they provided courtesy bus transportation to the Port of Miami. Then after my cruise, I would look for the rent-a-car courtesy bus and get on it. Then I would rent a car in Miami and return to Orlando.
I did this and it worked out great and I saved allot of money over parking it for a week at the Port of Miami.
Considering the rules of this website, I am not sure if I am allowed to mention the name of the car rental company I did this with. I will give you a clue... the name of the company is something that Texans remember; especially something that Texans living in San Antonio remember.
If I cruise again, it will most likely be on Princess cruise lines departing from Ft. Lauderdale. I hope that this car rental company also provides courtesy bus transportation from their facility in Ft. Lauderdale to Port Everglades.