“Something out there is putting its stamp on how the Milky Way turns. And that basic observation is what allows me to say that, with the help of some roof flashing and a paint-thinner can, I’ve been able to detect dark matter from my backyard.”
A $25 roll of roof flashing, an empty paint-thinner can, a $45 amplifier, and an RTL-SDR dongle. That gets you the hydrogen line at 1420.4 MHz and orbital velocities at six galactic longitudes. The curve comes out flat, which is the whole reason anyone thinks dark matter exists. The observation that broke twentieth century cosmology costs under a hundred bucks to reproduce in a driveway.