my airbag light goes on and off. on 2004 Chrysler Town & Country

what could be the problem and how much to fix it?

Well, it could mean that the emergency brake has not been fully released.The ABS system light is on if something has occurred within the ABS system. Something faulty may have happened there, get it checked out!
you need check out the code, I know for your car, the us703 scanner is useful.