Yes - the sensors are a bit expensive at about US$ 90 apiece but as I explained in another comment, I think that it has paid for itself

You can get cheap NDIR based sensors from aliexpress (around $20) such as MH-Z14A, which I've used with a Pi, via the UART interface. I just hooked it up to the 5V line on the Pi pin header and then used the Pis UART lines for the data, as that runs at 3.3V.