So, adjusting for inflation, that meal would be around $8.75 today. And with todays food prices, and today's higher minimum wage, it is still profitable.
NO ONE would pay $9 for this meal today, but we were paying $2.50 for it 2 decades ago.
A microwave hamburger patty is $0.90, a bun is $0.18, a gala apple is $0.65 - these are grocery store prices, not bulk orders from suppliers. But that comes out to $1.73 vs $1.75 ($0.50 adjusted for 20 years of inflation).
EDIT: As others have stated my inflation calculation is off by about 2x, but the point still stands, I can remake the same meal today at grocery store prices for less than the school meal cost 20 years ago when they were buying for 2000-3000 meals per day. There was definitely a profit being made on those meals. Along with all the other fees we were required to pay to attend our public school.