Mcdonalds different prices in same state https://mymcdonaldsmenu.com/

Why should they?

Are we assuming the cost to build a restaurant in Midtown Manhattan, get ingredients delivered there, and hire workers to make the sandwiches is going to be the same as rural Buffalo?

It's a bizarre assumption to make.

Locations don't all have the same rent or minimum/prevailing wage. Not saying there isn't funny business but we shouldn't expect prices to be the same for locations with different costs.