Think about how many weeks a year you want to work and how many hours a week Then add up all your expected costs - rent, electric, accountant, card machine, booking system, wifi, phone, water, commercial rubbish collection, uniform, advertising etc and then divide by the number of weeks in the year that you plan to work and then divide again by the number of hours you want to work. This gives you your costs per bookable hour and you add products cost to that plus your wages.
I've developing a business plan to reduce my client hours to 30 a week as I need time to run my business. To my horror my costs before products work out at £25 per hour. Eek. My plan to just see clients for 15 hours a week has been shelved!