You need a table with columns like
Account, StartDate, EndDate, DailyCost, DaysTotal, CostTotal
The formulas for DaysTotal and CostTotal will be (I used Table syntax for formulas, replace Table field references with regular ones in case you prefer this)
Code:
=(MIN(TODAY(),[@EndDate])-[@StartDate]) ' This is the formula for DaysTotal
=[@DailyCost]*[@DaysTotal] ' This is the formula for CostTotal