Business Use Case:
User with access to create a Sales Order has also the access to change the Unit Price in Sales Order > Items tab > Line Item > Price Level > Custom
By choosing the Custom Price Level, user can replace the existing price to the custom one. How can user not access the price level when entering Sales Order?
Price Level can be hidden in the form so any user won't be able to edit the unit price of an item.
A Standard Sales Order form shows the price level. Therefore, it has to be customized.
Uncheck the Show column of Price Level in Customized Sales Order form > Screen Fields tab > Columns subtab > Price Level