Other than the dealer, a good shop, particularly one that does body work, will probably have a code reader for the air bag system. You may be able to get the code read their more economically.
Likely culprits:
Clockspring: the steering wheel is constantly working that part.
Wiring under seats: junk shoved under the seats may have damaged the wiring.
In any event, if you work on the airbag system, be cautious and know what you're doing. Those things can be lethal.