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.
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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.)