Hello Mark

Thank you for your purchase.

It's easy to set the price of a service to be $20, but unfortunately, at the moment we don't have any membership options. We're looking into adding that as a feature, but until then I can offer a work-around.

You can create a service which would be named "Bulk Purchase" for example, and it would cost a certain amount. Then, you would need to create a 100% discount coupon which could be used 9 times, and limit the usage to 9 per customer, like this:

My advice would also be to enable the notifications, so they get an e-mail with the discount coupon, explaining that they need to use the coupon for the remaining 9 sessions:

You would need to add the %coupon_1% placeholder to the e-mail, so they get the coupon code they can use.

After someone books the first appointment, they receive an e-mail with it, and they use it to book the remaining 9 sessions.

I hope this helps.