Hitting an estate sale and lucking into someone whose tastes run similar to one's own can get a person whole libraries for cents per book. It's the kind of thing a certain kind of reader can dabble at for a few months one lazy year early in life, then stop and never do it again because they've accumulated a lifetime or more of good reading material for the cost of a very-few dinner-n-a-movie evenings.
(This is where many used book stores get the bulk of their stock, aside from, these days, buying out other used book stores that are closing)
(This is where many used book stores get the bulk of their stock, aside from, these days, buying out other used book stores that are closing)