Super wide, super fast and super sharp, this very enjoyable lens sells new at B & H for about $570 plus shipping. My copy has been barely used and is in great condition.
Includes rear lens cap, Sigma lens hood, and a Hoya, Super-Multicoated skylight filter -- a $70 filter -- that fits the unusually large, 82mm filter threads of this super wide optic.
I've posted large images of the lens at
http://billwisserphoto.com/clients/clients_special/20mm/Lens & filter together are $449 plus $15 shipping in continental US payable via Paypal.