If you choose to valet park, there is a fee of $12/day for that.
But once you pay for valet parking at one resort, you do not have to pay again that day.
Example: You go to the Contemporary for Breakfast one morning and pay for valet parking and then go to the Poly in the evening, you can valet there without having to pay again, just save your receipt from the morning.
One last thing, if you did valet park, say at the CR, you can then leave your car there for the day while going to MK.