Twenty years ago, I built a Geiger counter from a kit that I got from Electronic Goldmine.
Cost me around $50.00 US. Looks like they still sell kits in that price range ( $79.95), ok, that’s taking two decades of price inflation into account… You can buy raw Geiger tubes for as little as $15.00, so, if you are willing to build your own 400V DC power supply from junk box parts, it’s possible to build a Geiger counter complete with Arduino clone, for under $75 US.
“For a logging Geiger based off an Arduino, $800 USD seems really expensive.”
You are right. Even $550 is too much for a kit. And that’s US$…
Look up the Brogan kit and its evolution. Good history, good documentation, plenty of users (make sure to take a look at the enclosure gallery!) all over the planet.
You are right.
Speaking of fallout shelter. I have heard that by looking at spectrum from you can even find out what hits you - Indian nuke, American, Russian, Chinese or it was just a garbage from Homer Sipson’s garage etc. Cannot find examples of charts that can be used as examples. Perhaps looking at samples from respectful test sites would make it clear.