My general assumption for any food I'm getting eating out in the US (across a range of regions) is $20/person for fast food/casual, and $30 if it's a basic restaurant. The food will be listed at $7-12 etc, but the receipt will show twice that due to fees, add-ons etc.
IMO what matters is what you pay; the numbers they post on the menus and other media aren't useful.
This is from their online checkout, so it is what you'd pay.
(It doesn't seem implausible to me that you'd pay $20/pp for food in most parts of the US; I'm responding purely to the hearsay claim that someone paid $68 for 3 people. I can't square that unless you actually bought twice as much food, and then some.)
IMO what matters is what you pay; the numbers they post on the menus and other media aren't useful.