There is no "Incidental fee" at any of the couples resorts. They put your credit card number on file in case you charge things from the spa or gift shops to your room, but you don't pay any more than you spend.
they take a $300 hold against your card (credit or debit). I think they take cash as well. It's just incase you buy something at the gift shop/sundry store/spa/pictures/or make a phone call. If you don't spend a dime on property then you get it back.