Updating Costs on Open PO lines

I am working with a  customer that wants to run a process to recalculate the and reset the costs on their open purchase order lines because of supplier raw material costs change that will occur monthly,  Think of it as the commodity costs for metal changes at the beginning of each month and that new cost needs to be now on all open PO’s as well as using it ro reset the raw material’s standard costs and thus changes the standard costs of the products produced by that raw material.  I know individual purchase order line costs can be manually changed, but is there a process that can do this for a range of or all open purchase order lines?  Thanks!