If your intention is to take a private car/van to the port, you will save roughly $25 by going from the airport to the port rather than from a resort to the port. For me, that wouldn’t be worth the additional time it would take to bring my family and luggage to the Magical Express bus, take the bus to the boarding drop-off area at the airport (with possible stops at other resorts first), unload the luggage, and walk with it to get to the pick-up location.
You could save more by using a group shuttle from the airport to the port, but it would still mean a lot of juggling people and luggage.
If your goal is to arrive early to the port, your best bet is to take private transportation directly from Port Orleans.
If you are at least 3 days before your cruise, there should be no fee for cancelling the
Disney cruise transportation.