Need help with process flow for "pay what you want" coaching services

Site URL: http://www.somaticsoulutions.com

I'm a coach who offers my work 'by the month'; a month being 3-90 minute sessions. I also use a 'pay-what-you-want' model. My current set up is to offer a low, mid, and high price point for a month package of three sessions. Ideally I would offer a single package of three session and a client would be able to input the amount, pay, and then schedule the first of three sessions, rather than choose one of the three price points I'm offering. As far as I can tell there's no way to do this, nor a workaround I've been able to arrive to. I'm curious what ideas you have on how to accomplish this?

Thanks for your time,

Ken

Also, to add, I'm currently attempting to do this with squarespace scheduling.