A lot more than we used to think … or so we are told.  Turns out that the economists who study this matter are not so convinced.  Those interested in what the most recent literature review has to say on this topic should go here: https://www.cato.org/pub_display.php?pub_id=9850.  Short answer: If you believe the scientific narrative offered by the IPCC, we’re probably looking at the low-end of $3-$24 per ton of carbon emissions.