I have been almost completely un-involved with microwaves, except for a brief stint in the Air Force learning to service and repair a Ku band (16 - 17 GHz) dual radar system, and then later (very briefly) at 70 GHz for line-of-sight propagation studies. It's a fascinating world, frequencies above 1 GHz, and more and more amateurs are becoming involved as the industry moves away from mass-market microwave sensors towards other (cheaper) solutions. Look at how laser "speed guns" have replaced Gunn diode "radar guns" or how PIR (passive infra-red) detectors have replaced microwave motion sensors, the latter mentioned by Dave in a note on his schematic post. The Government still uses microwave motion sensors to protect against unauthorized access to highly classified facilities, but the civilian market chooses low cost over higher security.
This paradigm shift probably bodes well for the dedicated experimenter, as a decline in microwave R&D and manufacturing should "free up" some sorely needed test and measurement equipment at reasonable prices. The "maker movement" has also helped with the introduction and acceptance of 3D printed parts. You can now make wave-guide components at home out of plastic and then vapor-deposit or electroless-plate metal films on them. You can even go on to electroplate thick films if necessary for higher power handling capability. Still, for really significant power, you need vacuum tube technology and, AFAIK, the usual suspects are unobtainable inexpensively. I think most magnetrons, TWTs, BWOs, and such are either re-built after failure or discarded. Good luck affording to buy a new one for amateur radio frequency bands... or maybe I am wrong there. Chime in, Dave, if you have some recent information on availability of powerful microwave components for amateur radio use.