I think you have to expect to pay a premium for theme park snacks-- by this I mean 20%-30% higher (sometimes more) than off-site. Of course, this is relative as prices vary throughout the country (and internationally). I come from an area where cost of living is high, so prices at WDW don't seem as bad, but years ago when I took my college roommate from small-town Ohio, she was shocked by the coat of everything. She wouldn't buy anything and insisted that we leave the park to eat, even though I explained to her that time IS money in a theme park.
I have no pictures, but WDW snacks are more expensive than snacks a my local zoo, for example. However, they are also more varied and better quality at WDW. So I see greater value in WDW snacks at their price. I feel like a lot of common snacks and counter service meals are more expensive at
Legoland, and the quality there is universally awful-- definite advantage WDW.
Sodas are a place where you pay dearly at any theme park, but, since I'm discussing relativity of prices, I've paid more for a tiny bottle of soda in a Paris train station than I have at any theme park anywhere (including DLP). On a hot day, that Coke is welcome refreshment at any price, and value can be maximized at a few CS restaurants with free refill stations.
So I think the question of how much is too much is relative to where you're from, what you prioritize, and ability to maximize value-- and probably a bunch of other factors, too.