How do I get a running total?

I'm trying to build an online order form that is elastic, because the entries could be for one item or multiple items (up to 40). I need to have a running total on the page so the teachers don't exceed their budget. Right now I'm using the Configurable List widget for the order entry portion, but I don't see a way to get it to total. I tried using the Form Calculation Widget, but it's only letting me use the Configurable List widget as a whole, and not letting me choose certain fields to include in the calculations.

If I can't use the widgets for this then that's fine, but if I don't use them then how do I do what I need to do?

It is not possible to perform a calculation with the dynamic widgets, such as the Configurable List widget. 

If you want to perform a calculation, you should use the basic form fields. 

How to Perform Form Calculation Using a Widget