To some degree, the market dictates what you can charge as LeAnn indicates. I looked at your profile and saw that you are also a personal trainer. If there are no comparable classes to use as guidance, you can look at your prices as a personal trainer. Divide this rate by the average number of participants and see how that would work for you.
I have a mentor that is well know in the fitness industry and as her and I were discussing this same topic over the weekend, the one thing I can say is know your value. Average fee in the big city of Denver is $10 per person per class. IF you don’t get the response you are looking for then lower your price. Hope this helps. :0)