I will spend $30-40 on a book, but only if I really think I will use multiple quilt patterns from it (Bella Bella Quilts and one Carol Doak book). I have spent a lot on 2 Judy Niemeyer patterns and one blackwork quilt pattern.
Otherwise, I generally stick to either free patterns or ones that I can recreate easily. I don't need to pay for someone to tell me how much fabric I need, how many strips of this or that honestly. A lot of times that is what the directions are rather than any real new method.
I try to only buy when I am wanting to learn a new method.