"edit" ooops, as I read further I see you already checked kayak. my bad. Try North West Air, I think St Louis is one of their hubs. They have flights for your itinerary in the low $500's, but they all have one stop
If I knew the answer to airlines pricing policies, I would write a book and retire on the profits. I think even the people who set the prices are confused. What works the best for me is to go to kayak.com. You can check the prices of all the airlines with one query, then you go directly to the airline to book, saving the charges from sites like expedia and travelocity. My travel agent hates me now. I only use him for very complex trips. Sorry in advance for that comment shammy!
