A rental has a day rate plus a flat delivery fee. How do I budget it?

A vehicle rental is quoted as three vehicles for eleven days at the daily rate, plus one delivery charge, and the budget has to add up to that quote. Give the rental and the delivery fee one line each in the same Section, and the Section subtotal adds the two together.

Two lines, one Section

Add a Cost Item for the rental. Amount is 3 vehicles, Days is 11 and Fee is the daily rate. At 450 a day that line totals 14,850.
Add a second Cost Item in the same Section for the delivery. Amount is 1, Days is 1 and Fee is the charge. At 600 that line totals 600.
The Section subtotal reads 15,450, and it flows into the budget Total in the sidebar footer.

A Cost Item multiplies Amount by its days by Fee, so the multiplication is done by the line itself. Any one of those three fields can hold a reference instead of a typed figure: the day count can come from a Variable, and the rate can come from another line. Type @ in the field to pick it.

Two lines also read well for a cost controller. The rental and the delivery show as separate figures, each one named for what it is, and the Section keeps them together.

For a percentage instead of a flat sum

When the extra charge is a percentage of the line, such as a 10 percent uplift, drop a Markup AddOn onto the rental line. The AddOn carries the percentage and the line keeps its own rate.

Type numbers the way the fields read them

A field holds a number you type or one reference. Type amounts as plain digits with an optional leading + or - and a decimal point.

Type 1500 for fifteen hundred, without a thousands separator. A dot reads as a decimal point, so 1.500 is one and a half.
A decimal comma works: 12,5 becomes 12.5 when you click away.
An empty field resolves to 0, so a line you have not priced yet adds nothing to the subtotal.

Good to know

The placeholder Number or @ on an empty field says what it takes: a number, or a reference started with @.
To add an uplift on top of another line's value, reference the line in Fee and put the uplift on as an AddOn.
A Variable's own value box takes a plain number.