Latest quotations from foreign manufacturers; Purchase order price of previous purchases; Receiving price of previous purchase.
The choice of specific price is also based on the judgment rules of the price of material items when you try to calculate the cost, so as to finally produce your standard price.
Other BOM cost algorithms should also be calculated according to the standard.
Therefore, no matter what kind of system you have, you'd better learn its principle from your cost accountant in order to track the price and calculate it.