I fully advocate filling up shelves with interesting "you never know when" type stuff!
I have have no idea if this example would be any good - but for 50 USD if I were in the US of A I reckon it might be worth a play
https://www.ebay.co.uk/itm/Neotronics-F-E-M-Fuel-Efficiency-Monitor-Combustion-Gas-Analyzer/323661764022?hash=item4b5bbe95b6:g:5dgAAOSwLKhcK7TL
It could be total crap
But if you're friendly with your local indy / garage / dealership you might be able to get them to let you do a simple comparison calibration (i.e. chuck your sensor down the next tail pipe too and compare the readings on your 50 USD piece of horse **** with their multi-thousand dollar gucci gucci - if you're friends with the mechanic I expect they'd find it rather amusing)