You are able to view the current price of the item you are adding to your Purchase Order (PO) once you + Add it to the PO.
To add an item to the PO, once you've already created your PO for the project:
Go to the Order Details page to add items
Locate the Search Bar, under Order Details
Start typing the name of the item
After you locate the item, click Add +
The item will be added with a quantity of 1
Edit Quantity by clicking the edit (pencil) icon in the line item
Enter Custom QTY or add Measured QTY
Click Add
The quantity is now updated
Repeat the above process until all items are added
When done, click Next to complete your PO