After reading the review at https://breathesafeair.com/inkbird-iam-t1-review/ I thought the INKBIRD IAM-T1 sounded like a good value air quality monitor with many of the features as ARANET4 but much cheaper
This price with 20% off code is the lowest it's been so far in Australia AFAIK, just over a $100 delivered.
I ordered one and paid $0.99 extra to get delivery in 2 days time. Otherwise delivery is included in the price and would've taken about a week
A CO2 monitor is very useful. Be sure to open the window regularly; otherwise, you might be slowly suffocating without even noticing.