There is free (Magical Express) transportation from MCO to the WDW resorts. However, this won't get you to the port.
The cheapest way we've found to fly in the night before is to get a 2.5* Priceline hotel in the MCO area. For this, we typically bid $31-35 per night, but on our last cruise we had to go to $39. Add about $8-10 for taxes and fees. This included transportation to/from MCO to hotel and breakfast.
Either when you check arrive at MCO or the next morning, get a one way car rental and use that to get to the port. You can drop off the passengers and return the car or just return the car and have everyone take the free shuttle from the car place to the port. We've found the MCO hotels to be much cheaper than those near the port. We've also found 2 one way car rentals to be cheaper than free parking at a port hotel and keeping the car.
When there are 2 of us on a participating airline, we pay a little more for the convenience of the on board check in and luggage handling on the way home. If not on a participating airline, it might not be worth it to you.