A few years ago, I went down the rabbit-hole of measuring camera spectral sensitivity. Ended up with a Rube-Goldberg contraption that can cost as low as about $30US (although that doesn’t account for the recent spike in wood prices):
These are spectroscopes, shine a light in the back and a rainbow appears in the other end. Take a picture of that rainbow, use some software I wrote to extract the wavelenghs, and ta-da, a spectral sensitivity dataset for the camera. The one on the left uses an optical grade diffraction grating to do the rainbow, about $108US, the one on the right uses a cheap ~$5US grating printed on a 35mm slide. Their performance is within about 0.2dE of each other, and within 1 dE of lab-grade monochromator measurements.
I made the boxes with home-improvement-store sourced poplar, cut it with a carpenter’s chop saw to get the correct angles. The collimating slit is two razor blades, and the diffuser in both is $15US lab-grade, too inexpensive to buy the right thing rather than to cheap-out with with white paper or somesuch.
Made SSF datasets for all three of my cameras, and now these contraptions sit under my desk. You can read about the whole sordid endeavor here:
https://discuss.pixls.us/t/the-quest-for-good-color-4-the-diffraction-grating-shootout/19984/