If you frequent local cafes check if they have a leave one take one area. Free and on the honor system it is somewhat similar to a little library you do not have to do both actions at one but community support are how they work and stay stocked and neat. This is often a small shelf or window sill with a little handwritten sign not an actual part of the business but allowed within their space.

today

Better World Books is a great source too. And they accept donations!

today

Our local library always has 3 book sales each year. They are very popular with all ages! I always buy a few extra books at the sale, to give to my friends and family for birthday or Christmas presents.