Quite cheap flights to New York and other American cities are showing up on the system - for Delta Airlines - most online travel agents have the flights.. There is no advertised sale - so considering how low they are it is not inconceivable there is an error in the booking system. Occassionally prices do fall very low but this is a rarity these days ( Delta did do a promotion last year to launch their JFK flights ).
My advice is to book quickly if interested. If these are genuine prices other airlines might react.
I only looked at dates up to April 2008