For Fees:
Go to Booking → Finance tab → Price Breakdown.
Select the fee you want to update and click Edit Fee.
In the opened drawer, adjust the Associated Cost per Item (purchase price).
Click Save to confirm changes.
For Upsells:
Go to the Upsell page → open the Edit Upsell drawer.
Or, go to the Unit Type level → open the Edit Upsell drawer.
Update the purchase price and save.