When you shop around for rentals, the price stated will mean the cost to use 1 quantity of the item, for one "rental period". While rental periods vary from store to store, it is usually 2 days. Some stores may give you a discount for extended rental periods, like a weekly rate.
This cost also includes the cleaning, maintenance, storage, and handling of the inventory. While some may think renting a tablecloth for $20 seems unreasonable, the overhead for the care and maintenence of that tablecloth is a continual expense for the company.
The cost typically DOES NOT include set-up of your rentals, like setting up chairs, placing linens on tables or tying chair sashes. Some companies may offer this as service for additional fees per item.
Never assume anything; ask if you are not sure to avoid major miscommunication disasters at a point where it will be difficult to fix.