Cost transaction required for cost-plus pricing

We are using cost-plus pricing for specific customer sales orders. We would expect this to work as long as the item is cost enabled and the standard item cost is defined in that org. However, there is also a requirement that the item must also have a cost transaction in that org. Since many of these orders would initially create demand of that product in a given warehouse, there is no guarantee that any inventory (or cost transactions) would even exist yet.

Why is a cost transaction is required?

If it is required, can a cost transaction be created without after inventory balances or cost reporting?