The most likely loco would be JetBlue. Others could be ATA and AirTran. Southwest doesn't serve the major NewYorkCity airports. The legacy carriers often meet or beat the prices of the "cheaper" lines if you reserve well in advance and avoid peak days.
I have a reservation on American Airlines from Washington IAD to Santa Anna/Orange County/John Wayne SNA and return - in late July - for US$259, all taxes and fees included. Go out on Thursday, return Monday. That's less than six US cents per mile for the roughly 4500 miles! This is about the same distance as London to Israel and return.
I can remember a decade ago when $400 round trip to the West Coast was a big bargain. How times have changed.
seacue