Yongnuo released a new YN 100mm f/2 lens for Canon mount. The Nikon version should be coming out in the next few months. The price of the lens is around $170. Yongnuo already has two cheap DSLR full frame lenses: 50mm f/1.8 and 35mm f/2 (see review). Check PhotoRumors for additional information on the new lens.
Yongnuo lenses are also available for sale at B&H.