The local library had a book sale in which they were clearly just trying to get rid of a bunch. You could fill a large shopping bag full for a dollar.
I got a couple of bags full. It took quite a bit of looking but I got some surprisingly good ones including one which was full of 11X14 lithographs of famous paintings. They were all suitable for framing.
My best friend and I went to a booksale on Box Day. I don't remember where we got the refrigerator carton lid, but they told us, yes, that's just one box all right. We filled it up for three dollars. A mountain of books apiece. Of COURSE that was the day that I got a flat tire going home, and had to take all those books back out of the trunk to get to the spare.