Running Balance Query

Hello everyone,

I have a client that I'm creating an Excel for and I'm beginning to wonder if what she needs is even possible without her manually updating equations. I was hoping for a bit help. 

She needs a way to show deposit records received for multiple events, while tallying the total amount and outstanding for each event individually. The issue is that, as far as I can determine, creating a new column for Outstanding Balance will not work since there is not a "Total" column to pull from...which I can't create since events will be mixed in together.

I did consider creating a simple pivot table, which would easily show the total for the deposits received, however again, it leaves out the Outstanding balance. Setting up a new equation that is based on the pivot will do little good since the pivot would update as additional deposits are added.

A screenshot of the table as is for any visual thinkers is attached for reference. 

Any ideas?