I'm booked for a flight from Philadelphia->LAX on Thursday (6th), but something important came up just now in conflict. I booked through Hotwire and the cost of exchange+fare difference is $2000+. Is there any way to get out of this? I remember that when I was late for a flight a few times, the people at the airport simply put me on a later flight at no charge... is that the norm? Tickets are from United Airline. Any advice?