Scheduled Update of Default Return Cost (Script?)

We're looking to regularly update the Default Return Cost for all of our inventory items and locations on a regular basis. Ideally it might happen daily, but we're fine with weekly.

The scenario is we use Average Costing right now and want the customers returns to happen with a return cost that is the same as the current average cost(our costs change regularly due to our industry). Most Return Authorizations are created automatically through an integration with our Magento website. We figured the easiest approach was to start using the Default Return Cost and then updating the Default Return Cost for all items to match the current items Average Cost.