the pricing depends on two things, one being demand and the other the local market and competition.
Look around and see what other trainers in your area are doing for comparable classes. If you are unique and have already a list of people who want to participate, you may be able to charge a little more. Do you plan to run this as a course with a start and end date? Or will it be ongoing with people coming and going as they want to? A course tends to be lower priced per session because people make an upfront commitment.
Hope this helps.