Consignment Item PO price

Hi,

I have couple of question in Consignment process and need your expert opinion on handling the same..

1. Consignment item's price fluctuates on market condition. In this scenario, for each consignment, is it required to create BPA with the market price and create SPO to receive the same?

or Retro price can be used?

2. We use Average costing and is it possible to consume the item by lowest cost i.e. if 2 consignment exists with different price and how to consume the lowest price consignment?

Need your advice on handling this scenario.

Thanks in Advance, Arun