Real-time Input Updates in Edit Page with Relation Manager

I would like to update a readonly input on the edit page as I change the data in a Relation Manager. In my case, it's with numbers: I have two models, CashRegister and Transaction. In CashRegister, there's a field called closing_balance, and I want it to update in real-time as I add transactions through the Relation Manager on the edit page of the CashRegister resource. Could the same be achieved through a widget on the edit page or perhaps a card? Another example would be based on this screenshot from the Filament demo. Is it possible to sum the values of each product and display that on the same screen?