I'm in Washington state, and because I'm a high school student, I only charge $40 per month, for weekly half-hour lessons. It amounts to $20 an hour. And that's on the LOW end.
My teacher, however, is really phenomenal. She has taken college piano courses and enters us in competitions. Her tuition is about $100 per month for weekly 45 min. lessons.
So I guess it depends on how good of a teacher you are.