If your Inventory Item has a price associated with it on it's item page, then that price will be the default price that appears on your order's line items.
However, you may have worked out a deal with your client and want to edit the price per item that you're renting. Here's how you can adjust that price.
Go to the applicable order and go to the line items tab.
Click the green “Edit Order” button.
Double click on the Unit Price. It will turn blue and give you a field where you can edit the price. Press enter.
You will see the Line Item Price change to reflect your new Unit Price. Line Item Price is Unit Price multiplied by the Unit Price. Adjusted Line Item Price is the item's total cost after any fees or discounts that would be affecting it.
Click the green “Save Order” button.
Again, this will not affect the Unit Price of the Item on any other orders or on it's Item page.