How to Track Client Sessions

Hi everyone,

I was looking for some help/guidance for my personal training business.

I currently have a sheet that lists data such as: Client Name (First/Last), Date, Amount of Sessions Purchased, and the Total Purchase Amount

I then have a second sheet that tracks the clients sessions, as I add them in it automatically removes sessions from the total. 

Edit: I attached two photos for reference. Squared off in yellow is the info I would like it to track

What I was looking for, if it's possible, is on the second sheet, I have a section that tracks the session price that client is at, is there a way to automatically track this? 

For example, if a client has 20 sessions left, 

They purchased the first 10 sessions at a price of $40 per, for a total of $400

But the second set of 10 sessions, they purchased at price of $32 per, for a total of $320

I'm looking for a way where it knows that after they run through the first 10, it automatically drops the session price column to $32 from $40