As a personal trainer, my rate goes by a sliding scale of $75/hour. My clientele is wealthy and highly educated. As a kinesiotherapist, gerokinesiologist, exercise physiologist, and personal trainer, I also hold various certifications and have a 20+ year background in classical ballet. I have a given rate with institutions hiring me, such as a fitness center and a retirement residence, but wonder what to charge a company with 450 tenants wishing to offer fitness classes as an additional service to its tenants.
I agree with Joanne. You can also check and see what your expenses are and how much your time is worth. A couple options I would look into, are to either charge per person/class or if you are not sure how many people will be showing up then come up with an hourly rate which you are comfortable with and go by that. Always check the rates other trainers charge around your area and then come up with one that you think you are wotrh and still be competitive.