The money did lose value, but apparently the difference in cost, adjusted for inflation is not all that different: According to https://www.dollartimes.com/inflation/inflation.php?amount=0.65&year=1971 Adjusted for inflation, $0.65 (for a Big Mac) in 1971 is equal to $5.01 in 2024. According to Google, "As of July 2023, the average price of a Big Mac in the United States is $5.17." So the bigger difference must be the shrinkflation.