I tried to do this (buy an affordable priced, reasonably accurate meter) and, after probably after reading the same articles as you, reached the conclusion that there are no meters that are accurate and affordable.

So many seem to rely on automatic ‘calibration’ - which just seems to consist of “let’s assume the lowest sensor readings of the last while correlate to baseline atmospheric CO2”.

For a meter that’s never taken outside, this is obviously going to mean it’s reading too low all the time after a few ‘calibration’ cycles. And, worse, it's likely to be more wrong in less well ventilated spaces.