How much should you charge for private lessons?

My theory is this – find the person just above you: either in education, job, or experience and charge $10 per hour less.

For example when if the local bassist with a masters is charging 70 and you have a bachelors, charge 60. For me, I found out what the local symphony guys are charging or what the people I study with are charging and go from there. Sometimes it may be $20 less if they are a top notch performer. But I also have a degree in education and one in performance plus 13 years education experience.