Cheap airline tickets from NYC to Los Angeles?

Where can I find tickets for under $400, hopefully even under $350, for a round trip flight from NYC/Newark to LA/Burbank, departing between July 6-12 and returning July 22-August 2. I want the later the departure the later the return, obviously. Every flight I find is over $400 aside from the rare one that seems to only be cheap for one day.