In the Settings -> Item Prices, you can create pricing to attach to your inventory. Generally when you create a new inventory item, you give it a price name as you are creating your inventory.
However, you can create an item price that is used for more than one rental item. For example, if you have several "Combos" that you rent out (all the same price), you can create one price name and place several of your inventory items into that price name. In this scenario, if you change the price for one of those rentals, all of the prices will change for the price name. In the future, if you want to change the prices of the individual rentals, you will need to create a new price for each inventory item you have. In the screenshot below, you will also see what rental items are using that price name and also a line graph for a visualization of your pricing structure.