Bring Estimated Amount or Rate from Requisition to Purchase Order

I am working with a business that needs to enter the rate for each item every time they enter it into a Requisition because the rate changes so often. They have been using the Estimated Amount field to put the rate that they want for each item. However, once it gets to the Order Requisitions page, the Order Rate has the Item Rate from the record in it and the Estimated Amount does not follow through to the Purchase Order. So the person who creates the Requisition has to manually key in each item rate and then the person that