That looks like my budget! None currently on ebay but I'll keep my eyes open.
http://thesybersite.com/general/12mm-fisheye/
Add on ed: (Had to re-boot to fit another key-board!)
If you see linked article, there were two versions of the lens, and sold under variouse trade-names: Accura, Beroflex, Berolina, Panomar, Sigma, Spiratone, Universa, Upsilon, and Vemar. So if you go hunting, don't restrict search to just Sigma or Panomar. They wont come up that often, but they were aparently the more common ameteur fish so you are as likely to find one as anything else.
Turned mine up in the mid 90's at a Camera Fair I chanced on. Its the only one I have ever seen, and at the time, the only fish-eye I had ever seen 'for real'! Despite hours scouring through the second hand cabinets at all the local camera shops around Brum, looking for interesting stuff on M42, particularly UWA!
'Specialist' stuff is SO much more available these days thanks to the net!
But; worth adding to the wish-list and hunting out; WHEN you find one, it's genuine fish-eye for the price of made-in-china fish-eye-distortion filter.
Shame you're north'o'th'wall of you could of had a borrow.