Nikonos RS 20-35mm f/2.8 Zoom, $500 plus shipping
In good overall condition. The lens has lots of internal dust, zoom operates smoothly. LED in focus window lights up when mounted on D810.
Lens mount is in excellent shape. Front glass has some very subtle marks, unlikely to be a problem in contact with water. Rear glass is perfect.
I have no RS body to test with, but does take images in air at infinity, at f/22. (Remember, this lens is water corrected and will only focus sharply in water.)
I have no way of confirming waterproof status as is.
Lens caps are functional.
These are getting harder to find by the day, especially at a reasonable price.
This lens would be an ideal candidate for SEACAM conversion. The interior dust would be cleaned out during the remanufacturing process.
It could also be serviced and used intact with a Gates adapter for cinema work.
As an aside, I recently converted my Nikonos RS 13mm through SEACAM. The service was excellent and the final product stellar. I am using it on a Nauticam ND810 housing with a Nauticam/Seacam port adapter. It works great!