Authorized Rokinon dealer bestpriceoptics via eBay has the Rokinon 16mm f/2.0 ED AS UMC CS Lens for Canon EF-S for $249.99. This is an eBay daily deal.
This is the lowest price we’ve ever seen for this lens — this lens is a recent one, first was announced in June 2013. This deal has 8 of the 9 mounts available — everything except (unfortunately) Canon M.
This lens is designed for crop bodies exclusively, and will vignette if mounted on a full-frame sensor. You can check out a flickr gallery for the lens, or read more at B&H’s Explora. Other dealers (such as B&H) currently have this for $315-$370.