I got so sick of paying late fines, I just buy used books of new ones on sale. I love libraries and was going to make a donation to purchase new books, but after their last stunt, I invested the $500 in my own library.
I also used to go to the library sale every year. They tossed older books (that hadn’t worn out, they just weren’t “new” titles) and even had multiples of unread (and unstamped) books that they had been given that they never even shelved.
Average price was $1-3.