There is an Action "Create Purchase Orders" on a Sales Order. When this action is being called the Purchase Order is being created but the Unit Cost entered on a Sales Line is not being taken over. The Purchase Price Calculation is being triggered regardless of what might have been entered on a Sales Line.

If the idea around Vendor No. on a Sales Line would be implemented that would be a good basis for extending the functionality "Create Purchase Orders" as the Unit Cost on a Sales Line can be entered either manually or determined base on this idea:
https://experience.dynamics.com/ideas/idea/?ideaid=245c8877-635e-ec11-a3ee-0003ff45cecf