I have 2 thoughts running through my mind regarding your situation.
1. If you still don't have an ELM 327 adapter to check and clear your own codes, I must issue you 1 demerit. It's not like the <$15 spent on the adapter will only get used on the Mirage. You can use it on most or all vehicles, you have or are going to have. No need to go by a parts store to have the codes read, or play games with your battery cables. 1 DEMERIT! That'll learn ya...
2. My son's minicat on his RX8 remains to be working. It's been 6 months or more, no more codes. It looks like the bottom mini-cat in a previous reply. The one with 2 pictures, a small hole spacer on the top, or the bigger hole with a grid in the bottom picture. The one that worked for me was the bottom hole minicat.
If you're going to sell the car, it would be ethical to let the buyers know of the 2 issues (O2 whatever and the airbag code). If you're going to trade it in to a dealer, to hell with them, hide it. I saw the inner workings of some (Hyundai) dealerships. They are such horrible crooks, they make Las Vegas casino dealers look like daycare centers. I'm certain all American dealers (all brands) are equally as crooked as that Hyundai dealer.
I don't blame you for not wanting to drop big money on it, if you're just going to sell it.
__________________________________________
View my fuel log 2020 Mirage ES 1.2 manual: 42.5 mpg (US) ... 18.1 km/L ... 5.5 L/100 km ... 51.0 mpg (Imp)