TANSTAAFL

There ain't no such thing as a free lunch.

Probably it is used elsewhere, but I know it from The Moon Is a Harsh Mistress (1966) by Robert Heinlein.

Back in the good old days, the only people who were allowed to use computers were Trekkies and/or guys in the chess club. While it is not necessarily true that all Trekkies and/or guys in the chess club also read Heinlein, I would bet that a lot of them did. So most of them had probably heard of TANSTAAFL.

In the late seventies, if you went to a computer store, you were not greeted by a salesperson who smiled at you while mentally figuring out how much commission he could make off of you. You were instead greeted by a guy with a pocket-protector and a Texas Instruments calculator who just wanted to show you his new toys. He'd let you stay past closing so that you could finish the chess game you were playing with one of the computers. He wasn't in any hurry to go home. Sometimes a whole bunch of them would just stay at the store and order a pizza.

And there was all this really neat stuff in the store, but you probably couldn't afford any of it. When you finally told the guys that the computers cost more than you expected and the one you wanted was out of your price range....

I don't remember any of those guys just saying TANSTAAFL and expecting you to know what it meant.