Since booking through US Air on the flight you want is $100 more than what you have already paid, I would call back to AJ again and request that they put you on it. Air J has to to decide whether or not to pay US Air their prevailing rate, and it is the supervisor on duty's call. Perhaps you will get a different supervisor who will take it. If not, I'd tell them you're going to think about your options and simply hang up. Try again a few days later and keep trying until you get the answer you want. Worst case scenario is you have to end up taking the refund and book your own flight, but persistence should eventually pay off.