(Meticulously pound them in before starting the sander.) Machines that eat material may run up a supply bill that exceeds the rental fee. The clerk should be able to give an estimate.
Get a time estimate too, allowing extra for adventures in learning. You should also allow for time lost to breakdowns of abuseable equipment such as ditchdiggers. The rent-it won’t charge you for time lost due to breakdowns that aren’t your fault, but they won’t pay you for your lost Saturday either.
When renting, a flexible attitude is appropriate. That, with a bit of luck, should get the job done for less money while increasing your independence. That’s a pretty good deal these days.
