You can get a good CO2 sensor for less than $50 [1]. For large-batch orders the whole device can be less than $50 [2]. Where are you getting an almost $300 addition to the base price?

[1] https://sensirion.com/products/catalog/SCD30

[2] https://www.ikea.com/us/en/p/vindstyrka-air-quality-sensor-s...