I am not sure about the ins and outs of Priceline bidding for one way rentals or non airport drop offs, but I have cruised out of Miami and I remember many of the rental car companies had downtown Miami drop offs with free shuttles to the port. I have a couple more things for you to consider, just to confuse you even more. You could look for a cheap hotel, Priceline could help you there too, near the Miami airport. That way you could either drop your car off at the airport car rental and take a taxi to the port for about $30. Or, you could look for a hotel with free parking, keep your car until the morning of your cruise and return it downtown and shuttle to the port. It does make some sense to me to break up your rental the way you are contemplating. Since you will be in Orlando for a good chunk of the time, if you can get a cheap Priceline bid for that portion of your trip you will probably be cheaper off in the long run. It seems like a real headache to me to have to drop off a car at one rental company and get to another one if you have off airport locations. I am not that familiar with MCO to know how many rental companies are on site. You could end up taking a shuttle from one rental return back to he airport to pick up another shuttle to your next rental company.