If you are into a hobby, how much money do you put towards it?

I'm really into reading, and it's great that the library is easily accessible, but I kind of like to collect books and keep them as part of my hobby. Unfortunately books can get pretty expensive! Some months I don't buy any but some months I spend $30-$50. Of course some of this is part of gift money. I wish hobbies weren't so expensive, but luckily it gives me hours and hours of entertainment.