I use to teach Zumba at sports and health, but now I just want to do my own format and rent out space (banquet hall). My class was between 50-70 people. Some were turned away just because the class was so packed. However, im not sure how profitable I would be. Im thinking about starting out 3 times a week for about$6-7 per class.
Another factor to consider is whether the other class you taught was at a gym where people paid a membership fee that included classes, or whether they were paying per class. Some students will follow a teacher they love and pay a fee for the class, but others will not want to pay extra if they get something similar for what they are already paying, even if it is for a really great instructor. It might be interesting to just ask casually around to see how many people take other classes outside of the facility currently.
It might be helpful to do a cost analysis, as Janet suggests: compute what it would cost you, compute the time you need to spend each week off the floor on things like marketing and travel, and so on. Do some research to see what other teachers teach stand alone programs in your area, and visit a few to see what sort of numbers they get.
It can take time and a TON of work, but it is possible to make it going solo, as long as you are thoughtful about setting out, and do not have expectations that it will be immediate.