I think the cheapest transportation to/from the port depends on the size of your party. If you have a group of 4, I think it is cheaper to do one-way rentals thru Avis. I usually get a full-size car for about $45-50 each way. When renting a car, remember to get something large enough to accomodate your passengers and luggage.
You can use Priceline to find a hotel near the Orlando airport for about $40, or you may be able to find a promotional code to use for the Radisson at the Port for about $59-69.
Have a great Cruise!