Is the construction of an etalon / Fabry-Pérot interferometer within the reach of amateur telescope makers? Are there any resources pointing to such projects?
If it exists, some ATM somewhere has probably attempted it! The two main manufacturers of solar telescopes, Coronado and Lunt, both started out as small mom-and-pop operations, so I think building an etalon is well within ATM capabilities.
You can buy etalons on eBay cheap, they even have some 1" 1047nm for $35 now. I am a holographer, and I know how to use these in a laser. What confuses me is how they are used in a telescope with converging, rather than parallel rays. Can you just put mylar and a long pass filter (maybe a couple lighting gels) in front, place the etalon on a gimbal mount in the path, and put a camera on the end?
vol. 3 of the Amateur Telescope Making series has details on how to build a narrow-band filter for solar observations.
I did not attempt to build it myself, but looks very interesting.