If you want to see the actual purchase value or amount before the items are sold, you can run the Purchases by Product/Service Detail Report. Here's how:
Go to the Reports menu.
Look for the Purchases by Product/Service Detail Report in the Search bar.
You can also customise the report if you want to filter it by item. Just click the Customise button in the upper-right hand corner, then go to the Filter section. Once done, check the Product/Service box and select the item that you want.
Here's an article about customising or running reports for more reference: