MIGO receipt only requires an info record, but it does not do much with this info. A liability based on the info record price is only created if you goods issue from your consignment stock or when you move it to own stock.
So in general you could order consignment stock to fill-up your warehouse stock (if I understand correctly, then you keep the stock until it is sold via the auction.
When the auction is over, you probably create a sales order.
Based on this sales order you know the price and the quantity.
Now you can create a standard PO (do not send it to your supplier)
you cancel the consignment receipt (movement 102) for the sold quantity .
and create a new receipt for the new standard purchase order.
then you deliver to your customer.
you see there is an extra step with a second PO, a cancellation of the initial receipt and a new receipt. 3 steps more than normal. Those steps could be optimized (e.g. an IDOC from the sales order could be used to create the standard purchase order, a scheduled z-report could create the second receipt using BAPI)