I have too many ultra-wide angle lenses, so decided to let this one go. It's a gem of a lens, and works great on the A7 family (you'll need an appropriate adapter.)
Voigtlander 12mm ƒ5.6 Ultra-Wide Heliar II Aspherical lens for m-mount
$549 including PayPal fees and shipping to CONUS addresses.
A recent shot with this lens on the Sony A7S-