While you probably can't find the official Canon BG-E11 battery grip for the Canon 5D Mark III at $350 US dollars (seen here), The Pixel brand is already claiming to be working on an 'Alternate' BG-E11 battery grip for about $90 bucks. [Thanks Joel].
The Pixel images so far look very close to the original BG-E11 design including the small joystick button and rubberized coating (according to their description). The listing via eBay is posted as a Pre-order to be released June 10th. Check out more of the images and information following the link (click here).
Canon 5D Mark III (alternate) Aftermarket Battery Grip BG-E11