A basic hamburger is about $8, a combo meal is about $11. That includes fries and a soda. Outrageous!
Buy a reusable soda jug there. it's $7 or so and it comes with $1 refills all summer long.
I live about 20 minutes away. I'd suggest eating out of the park, then coming back in to the park later. Don't forget to get your handstamp!