Hi,
Looks like you will know the actual price of your goods when you receive the goods at your doc.
You can go with the standard process with purchasing info-record maintain the validity as per your requirement.
Here you set the price control as "5" so that every time the Goods receipt are updated as per the info-record price what you had update during GR in info-record and it will not consider from purchase order.
Kindly revert back , if you are looking any other functionality.
Rgds,