Auto-email report to Sellers when Opportunity has zero value

Hi- a number of our sales reps are creating opportunities with zero value.  On occasion this is deliberate, the opportunity simply can't be quantified yet, but usually they simply forget to add a value.  Is there a way to create a workflow (?) to send out an auto-email to the owners of opportunities with zero values on a weekly basis with links to the questionable opportunities?  For some reason I'm blanking here.  Any help would be appreciated!