Purchaisng Out of Print Books?

My landlady told me about a book she used to love to read her kids/grand-kids called "Brenda Brave Helps Grandmother" by Astrid Lindgren. I did a quick search online and found that it is out of print.

Does anyone have any idea where to find out of print books for sale at a reasonable rate?

I already know that a movie was made but I am looking for the small Golden Book style.