As the others have stated, take a look at what you need to cover your costs, what you want to net and then set a price. You can also see what your competition is offering for some ideas on pricing for your area and package ideas.
You may also want to consider adding a “unlimited” monthly package to your punch card. You can keep the punch card and add a “unlimited” pass to for the month. Clients can attend as many classes as they’d want and they would get billed monthly through an automatic ETF. They sign a contract allowing this and notifiy you in advance when they want to cancel, usually a two week notice.