Edit price while creating order
If you want to change price while creating a rental order, this may be done in the Sales Order (COA) document. In the COA document you will see the link to the Price Agreement (PRA) document on the item line.
Press the PRA link to enter the price agreement document. Press the folder called Recurring and highlight the relevant price. This will prompt a popup where you may edit details. Any change here will apply to all the items in the order.
If you want to change the price in specific periods of the rental agreement, you may press the Create New icon down in the left corner while in the PRA document (and in the Recurring tab). Here you will be presented with a calendar application and price, and you can modify this as you please.