If you are staying onsite, parking is free. Guests visiting from offsite resorts pay $10.00 per day. This fee is only paid once per day, if visiting another park, show the CM at the tollbooth your paid receipt to avoid another parking fee.
The main car parking opens quite early, infact it's just about a 24 hour operation now. CM's man the tollbooth at around 6-6:30 am. If there is no CM, then you are directed to proceed to your destination (there are signs there stating this) The resort monorail starts between 6:30 and 7am. The ferry starts at 8am.
The bus is an excellent option for visiting MK. The breakfast bus starts between 7 and 7:30 and the bus drops you off AT the Magic Kingdom. There is no need for ferry or monorail when using the bus.