Earlier quoted context omitted.
One other thing to compare is business and health regulations. Compliance with that is certainly more involved and costly today than in 1940 and would account for part of the price.
I'd love someone to build a tool that shows the price of that burger, say, and breaks it down to the input cost. Burger: $5.00 ---------------- Meat: $0.20 Bun: $0.05 Staff: $0.25 Insurance: $4.50
You're getting very close to wanting to reinvent the Economist's Big Mac index: https://en.wikipedia.org/wiki/Big_Mac_Index