Create a field that totals up dollar amounts from invoices that are assigned to a specific agency

I have a similar question, I have an expenses table our field guys enter their expenses into daily. I need the "Food" dollar amounts not to exceed $40 a day and "Parking" not to exceed $10 a day for reimbursement purposes.

I don't want to use form rules because I think people will be adding these in grid edit most of the time. 

Can I create 2 fields one to total any expense amounts in the food category for one day and then another field called expense payout total to be either the daily expense total or $40 whichever is less.