i've tried to make this calculation without much success. And that's after 50+ visits.
it's very variable depending who's on the trip.
when it was just me, i spent very little...i had very little inside the parks, had my main meal at sweet tomatoes (yum)....
When it's with DH, DD, DS - it was a lot more...(meals onsite, grocery runs for snacks and breakfast fixins, snacks through the day in the park, etc etc)
now that it will be with DH, DD, DS and spouses and kids, heaven only knows....the skies the limit i fear.
bottom line, it's hard to calculate...
but the suggestion by a previous poster about going into menus and trying to figure out what you would order is a good one..