There Ain't No Such Thing As A Free Lunch
The acronym is used as the title for the third part of The Moon is a Harsh Mistress. The particular reference to a bar that serves free lunch but serves expensive drinks.
This is an allusion to bars and saloons that served free meals but charged high fees for drinks. For some reason this comes up in economics classes to encourage students to understand that whenever something is "free" the hidden cost is factored into something else. But somehow they always fail to recognize that the paid for portion is intoxicating, while the gratis portion is nutritious.
I haven't thought to much through this, especially not in terms of the economics of the book, or reality.