How much should I charge to be a tutor?

I am a junior in college, studying to be an elementary teacher. I will graduate in a little under a year. I already work in my college's tutoring center as a math/stats tutor for other college students. The director of the center told me about a woman that approached her asking for a math tutor for her daughter who is sopre in high school, and taking algebra II. I go to school in a smaller town outside of Omaha, NE and would probably be tutoring either in my school's library or in their home. What do you think is a reasonable rate to charge? When the director of the center told me about this family, I did not get the feeling that they made a lot of money. I don't mind charging a little less than average so that they can afford to have a tutor if needed, but at the same time I do not want to get ripped off. Thoughts?