I created a new item. When I added it to a Purchase Order, I got the notification: "Lutron RRD-6ND-WH is not in the price list CES. We've applied the default rate specified for Lutron RRD-6ND-WH. OK".
You should also provide the option to add the item to the price list! This option should be provided right then and there, so the concept is fresh in the user's mind.