The Economist has the Big Mac Index which tracks the price of the Big Mac. The most recent average is $5.69.
I also have my doubts about the 1980 price listed here. The index started in 1986 at $1.60. I can't imagine it more than tripled in 6 years.
That's the national average. Obviously prices vary a lot depending on the McDonald's location. But so does the minimum wage. Franchisees set their own prices, McDonald's corporate only has some limited ability to set promotions and nudge.
Also I don't really know the value of such a comparison beyond arguing for the federal minimum wage to be increased.
Americans spend less of their income on food these days (even with recent inflation) than they did in 1980. Largely because grocery prices have generally lagged behind overall inflation and wage growth. Eating out on the other hand has increased. It is one of the better stories of the last century. People used to spend like 20-25% of their disposable income on food. Now it is like half that.