I have a couple of Apollo Air-1 sensors with CO2. Wifi not zigbee. Highly recommended. If you look at the individual part prices they are not making a lot of profit.
If you are into DIY you could make your own for a bit less using ESPHome (surprisingly easy).
Particle, VOC, temp and humidity sensor SEN55
CO2 Sensor S8 004-0-0053 or SCD-40
Temp & Humidity SHT41 (or just use the SEN55 temp and humidity)
Pick an ESP32 from the recommendations here: What's your favourite ESP32 board? (# Best, good, cheap, quality, reliable)