Make the assumption that you will be off the ship and clear customs by 8:30 am. You may have to wait for the Budget shuttle, then the time of the ride, and loading and unloading luggage. Assume that takes 30 - 60 minutes.
Now, you need to get the car at Budget. Assume another 30 minutes to finalize the reservation and get luggage loaded.
So, you should be on your way to MCO by 10:00 am, and it is an hour drive.
Drop off the car and get to the ticket counter may be another 15 minutes.
11:50 is possible, but it might be tight. You are very dependent on all the shuttles. If you luck out and catch them all, you will do great. If you just miss all the shuttles, you may be a nervous wreck.
Can you get a car service to pick you up? That would save all the rental car time, and you could be at the ticket counter by 9:30. Or use
DCL transfer just for the trip back.