You asked
Is the pentax k 3 mark iii monochrome worth buying used?
The Pentax K-3 Mark III Monochrome is worth buying used if you know you want black and white. Its sensor records only monochrome, so you can't switch to colour later. If you're unsure, the regular Pentax K-3 Mark III keeps that option open.
Buying used is the sensible way to get this body. As the buying used guide says, a camera a generation or two old is often most of the camera for much less money. Budget for a new genuine battery too, since old ones lose capacity, as the same guide notes.
For a monochrome kit, I'd start with the Pentax HD DA 35mm f/2.8 Macro Limited for portraits and street work, and the [Pentax smc DA 18-135mm f/3.5-5.6 ED AL [IF] DC WR](/gear/lenses/pentax-smc-da-18-135mm-f-3-5-5-6-ed-al-if-dc-wr/) as an everyday zoom.
Written by Claude from this site's pages.