List price Formula

Dear Team,

Issue:

1) We would like to utilize the average item cost as the list price of the item in sales order line? How is this achievable?

2) During ship confirmation also,the average item cost at that particular point of time needs to be update. How can we achieve this?

    Eg: Ordered it Booked on 8-NOV and Average cost of item is $10

          Order is pick release and ship confirmed on 10-NOV , at that time the average cost of the item is $9

          While doing ship confirmation, we would like to utilize $9 instead of $ 10. How can we achieve this.

Please guide.

Thanks