Probably the cheapest CO2 sensor and works with HA.
Can be integrated locally via HomeKit controller
https://www.home-assistant.io/integrations/homekit_controller/
https://allegro.pl/produkt/czujnik-temperatury-netatmo-healthy-home-coach-alarm-swietlny-lacznosc-z-wifi-fd520be9-8929-465b-bb47-aed692fc3da0
https://developer.legrand.com/solutions/smart-indoor-air-quality-monitor/
https://www.netatmo.com/en-gb/smart-indoor-air-quality-monitor
https://www.euro.com.pl/czujniki/netatmo-healthy-home-coach.bhtml
https://www.home-assistant.io/integrations/netatmo/
https://hejdom.pl/blog/40-netatmo/251-netatmo-miernik-jakosci-powietrza.html
https://forum.arturhome.pl/t/jakosc-powietrza/247
249 PLN
https://allegro.pl/oferta/outlet-netatmo-healthy-home-coach-miernik-jakosci-15370543276
Inside photos
https://fccid.io/N3A-NHC01/Internal-Photos/Internal-Photos-3138292
Info about LED color
https://helpcenter.netatmo.com/hc/en-us/articles/360015925951-How-to-understand-color-codes