What does the extra shoot day actually cost, in money and percent?

When the client decides on the delta and not on two totals, build the five-day version as a scenario beside the four-day one and the number is already on screen. Every scenario column header carries that column's own total and, beside it, its difference against Main. A two-button toggle switches that difference between a signed money amount and a signed percentage to two decimal places.

For example, Main totals 84,000 for four days and the five-day scenario totals 98,700. The header reads +14,700, and +17.50 percent after one click on the toggle.

Where to read the number

In the budget editor, in the scenario column header. The right-hand figure is that scenario's own total in the budget currency. The figure beside it is the difference against Main, and the toggle next to it flips between the money amount and the percentage. The Main column carries no difference figure, because it is the fixed point everything else is measured against.

The difference is the scenario total minus the Main total. A positive number means the scenario costs more than Main and is drawn in red, and a negative number means it costs less and is drawn in green.

Per chapter, in the sidebar. Once a scenario exists, the sidebar Sections tab switches to a compare view listing the difference for each Section, so you can say where the extra day lands and not only what it totals. A toggle above the list swaps the whole column between percentages and amounts, with the tooltips Show percentage change and Show absolute change.

In front of the client, in the Offer Document. Insert a Scenario Comparison block and it prints the two versions side by side with a Difference column against each Section and the grand total. That is the version the client reads.

Good to know

The Difference column in a Scenario Comparison block runs the other way from the column header. It is the base side minus the comparison side, so with Main on the left a positive number means Main costs more and the scenario is the cheaper option.
Column headers always measure against Main. To measure one scenario against another, use a Scenario Comparison block and pick both sides yourself.
Both sides recalculate as you type, so the delta stays right while the brief keeps moving.