Hello and thank you for trusting us with your question. I'm DJ.
Did the mechanic do anything more than checking for codes? You could end up replacing the air bag and still have the same problem.
There is a part called the clock spring that is much more likely to fail than the airbag and the cost is much cheaper to fix it.
The proper way to diagnose this is to remove the airbag, put in a shunt where the airbag normally plugs in, then run the system and see if the code returns.
If the failure codes returns, then the problem is the clock spring. If the code goes away, the problem is the airbag.
If you buy a used airbag, be very careful. I've seen airbags that have deployed, then patched up and sold on Ebay and Craigslist. They only work once. Only buy from a reputable recycler, never a private individual.
Doing the correct test should cost $100 or less. It could save you $1,000 so it's worth it.
Please let me know if you have any questions on this or if there is anything more I can do to help you.