Superwide lenses for the Canon FD system?
I recently found myself in a situation where my FD 24mm lens wasn't wide enough. Because I expect to do more shooting of that kind, I had a look around for superwide fullframe (no crop circle fisheye) lenses. Canon made 15mm and 17mm superwides, but they are rather expensive. I could get the 20mm f/2.8, but I'd prefer something even wider.
Are there any good third-party superwides available for the FD mount? Maximum aperture doesn't matter, I just need a sharp piece of glass for a good price.
What are your recommendations?