A couple of important distinctions: When we talk about Fast Food, there are different definitions usually defined by entree price points.
The lower tier Fast Food chains are defined by average quality and a fairly low cost menu. These include McD's, BK, Wendys, Arby's... average main entrée item cost < $ 4.00 per item.
The next tier is what the industry terms: Fast Casual
https://en.wikipedia.org/wiki/Fast_casual_restaurant
This is the realm of Chipolte, Shake Shack, Five Guys, etc. Different price point: $5 - $ 10 for main "entrée" item..
As you can see by this discussion, we are comparing apples/oranges. Interesting fact - the $0.99 Cheeseburger on a Dollar value menu costs the restaurant $0.94! The margin on this item is $0.05... this is why the beverage programs (soft drinks / coffee etc) are so important. Interesting fact #2 - typical fast food/c-store coffee... < $0.21 cost of goods (12 oz) - coffee / cup / lid....