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Item: Sigma 400mm APO Tele-Macro (77mm). I have NO connection to this (I know nothing about the seller or the lens beyond what the ad says) and I have my own that is NOT for sale, but I just bumped into one for sale on eBay in the US on a 10 day auction so I thought I'd post it since these almost never appear anywhere.
Price: auction (just starting around $200)
URL: Sigma AF 400mm F5 6 APO Tele Macro Lens 77mm Case Fits Pentax | eBay

The autofocus gears on mine "stripped" (really gear posts loosening so traction is lost), as they did for "Yuri" (from NZ, if I remember correctly) who bought one around the same time I did and this seems to be a common Sigma problem, not just for this lens. This has brass, not plastic gears like many of the Sigmas that apparently strip. I did fix mine (at the cost of the ball-detent on the MF/AF ring stopping working and then losing the ball in the carpet) and Yuri got his fixed in a shop. So be aware that could be in your future, but you don't need an unobtainable replacement set of AF gears.

[Des]

At $117 USD for the lens (shipping $37USD) I'll be getting what I paid for ! lol In fact I'm not entirely sure it'll have a K-mount, it wasn't advertised as any mount, it looked like it was K-mount from my intense looking. If it turns out to be something else, I'll just change the mount, I've got a few dismantled K-mount lens "filangies" lol.

If you are that handy, you might do a little sideline in buying good cheap MF lenses in other mounts and converting them to K mount! People have thought of this before, especially for Canon FD lenses: https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/96625-canon...questions.html
A Canon FD 400mm f4.5 adapted to K mount (especially with stop down metering) could be interesting.

[zoolander]

If you are that handy, you might do a little sideline in buying good cheap MF lenses in other mounts and converting them to K mount! People have thought of this before, especially for Canon FD lenses: Canon FD to Pentax conversion questions
A Canon FD 400mm f4.5 adapted to K mount (especially with stop down metering) could be interesting.

Yeah I know . Here's to being a cautious shopper lol !

But its okay, an adapter won't cost must, I just want to get out there and have a little fun for cheap for the time being. I've had enough of trawling.