Esslinger currently has the GRS Benchmate Basic Package on sale for $185.00.
The GRS Benchmate is a mounted ring holder that allows ergonomic positioning of a ring clamp for setting stones, engraving and other operations. The basis of the system is a tapered dovetail plate that is attached to the front of a jewelers bench. The mount slips on and locks in place in seconds. The height is somewhat adjustable and the ring clamp is fully adjustable so it can be mounted plumb or at an angle. The ring clamp swivels in the holder as well allowing access to every side of the ring settings.
While a bit pricey, they do seem to have great popularity with bench jewelers. There are a host of accessories available as well. The manual details setup, adjustments and maintenance (.pdf).
GRS Benchmate Basic Package [esslinger.com]