After finally getting a chance to use these monitors hands-on, I think the Apollo AIR-1 and Temtop monitors both deserve a place on this list.
Firstly, the Apollo AIR-1 is a relatively inexpensive air quality monitor that begins at $90 (for PM, VOCs, NOx, temperature, and RH) and goes for $110 if you include a CO2 sensor. There is another variant at just under $150, but I don’t recommend this for the reasons I explain in the article.
It’s worth noting that if you want to use the Apollo AIR-1, you will need Home Assistant running on your local network.
The Temtop monitors (I tried the M10+) are also decent, affordable options, depending on exactly what pollutants you want to measure. Please check out the below thread for more information: