I think it’s like, “You get what you pay for.” but I’m not really sure either.
It’s a classic simple joke probably decades old, but the humor is in the implication they want a bigger portion of something bad. Edit: ah it seems to be from the Woody Allen movie Annie Hall: https://www.goodreads.com/quotes/4151-there-s-an-old-joke---um-two-elderly-women-are
There’s an old joke - um… two elderly women are at a Catskill mountain resort, and one of 'em says, “Boy, the food at this place is really terrible.” The other one says, “Yeah, I know; and such small portions.” Well, that’s essentially how I feel about life - full of loneliness, and misery, and suffering, and unhappiness, and it’s all over much too quickly.