several car rental companies have shuttles to take you to their port canaveral sites. or you can take a cab and 2 that I know of will reimburse you for the fare up to $20 to thier sites.
I will be doing this May 13th. My flight home from MCO doesnt leave until 6pm and It is handy to have a car for the day. Hertz gave me a rate of $69 AAA rate for the day. Its more expensive becuase I am dropping it off at another place. this is some infor my wonderful travel consultant had sent to me and I hope it helps!
National 321-783-7575 (They will reimburse - a portion of your cab fare to pick up the car) no shuttle apparently.
Then 2 companies have a shuttle from the Port to their pick up location:
Avis: 321-783-3643
Hertz: 321-783-7771