The core device is typically on the order of $50-$150 US, but with many of the sensors that CO2meter sells, you're also getting a microcontroller, display, power supply, etc. You'll frequently find temperature and humidity sensors and also barometric pressure sensors rolled into that, since NDIR is affected by all those things.

So the price of a good, fully realized NDIR CO2 meter is comparable with any low-volume, moderate precision, moderate complexity electronic device.