Hello Wallace - I got a used CO meter by Gunson (Gunson Gas Tester Professional) - I don't recall what I paid exactly, but probably it was around EUR 150. I calibrated it against a proper garage CO meter and it proved quite accurate. I like knowing from a true CO meter where the car is, although it only measures CO at idle. As you probably know, the FI pump has different settings for idle, partial and full load. I believe the BBB calls for CO readings while driving, and shows photographs of a CO meter sitting in the passenger seat while the car is on the move. So although I know and can influence the idle CO, I can only hope that the FI pump is able to maintain the proper settings at operating speeds.
If you search on Ebay or Google for this Gunson apparatus, you should be able to find both new and used units.