I really liked this article until I went out and looked at how much Leica M2s cost. The project may only cost $100 in Raspberry Pi parts, but it looks like acquiring a Leica M2 can cost thousands of dollars.
You can always take the soviet rip-offs like the Zorki 4 [0]. Price is around $50 (at lest the last time I checked). I have one (it was my first cam gifted to me back in the 1980s by my father) and it still works very well. Though I nowadays tend to adapt the Jupiter 8 lens I got on it to my Nikon Z6. :)
Zorki cameras are Leica II/III(aka D2/D3) clones with LSM/L39 mounts, which don't take later M-mount lenses, though M series bodies(M3-M7) takes LSM via an adapter. Also they're not real Leica in case you care.
Indeed - that made me laugh. I've a single ZM lens left over after I sold my M9 and I'd really like to get it back to active duty. The price of ANY M-mount camer body is excruciating.
I really liked the project info regarding shutter speeds etc, and I'm considering trying this out with a Nikon FE2 I don't really like and picked up for £100 some years ago, but I suspect even these cameras have gone up in price. I might make another pinhole camera for the RPI sensor, that can be done with an old body cap and any camera-like box.
Speaking of Nikon, the Nikon F2, a fantastic, fully mechanical[1] SLR, is widely available on the used market for <$500 and compatible with nearly every full-frame Nikon SLR lens ever made with an aperture ring[2].
My current personal favorite "vintage" camera is an F2 with non-metering prism, type H full-field microprism viewing screen, and 50mm f/1.2 lens (still a current[3] Nikon product!), mostly because it has the clearest, brightest, largest viewfinder image I've ever seen on a 35mm camera.
[1] Other than flashes and optional electronic metering prisms.
[2] The only exceptions I'm aware of are the PC-E tilt/shift lenses, which have "soft" physical aperture rings that still require electronics, and therefore power supplied via the lens mount, to actually stop down the lens.
Also, my claim only fully applies to non-metering F2 viewfinders; metering prisms protrude a bit from the front of the camera body and interfere with the mounting and/or operation of certain lenses (including, I believe, all PC lenses).
I had an F2AS for many years, excellent viewfinder indeed, 0.8x, the same as non-HP F3, but quite a beast to carry around. The ME Super had even bigger magnification but probably not a 100% coverage screen.
I only sold the F2 motor drive last year, and that was ridiculous too, ten AA batteries for the MB1 battery pack. Cannot believe I used to take that thing to parties for kicks 20-30 years ago.
