Sharepoint list show total per item

Hi,
Im working on an inventory list at my work and want the user to easily see the total/balance for every item. Right now I have them grouped per category which I like the most but then the total sum doesnt work and if I group them per item the list gets too long. 

1. Is there a way to show the total of a group when its collapsed? That would do it for me.

2. Or, is it possible to create a calculated column that shows the current balance for every item without showing the records (transactions), so it becomes more like a pivot table like in exel. See attached

image. 

Does anybody understand what I want to achieve 🙄?