The launch cost per Antares 130 is about $240m from one of the NSF Orbital threads.
That's very high. The entire contract for Orbital is 1.9 Billion and that includes Antares, Cygnus, operations, etc. With 9 originally planned flights a $240m Antares alone would have cost 2.1 Billion.
EDIT: Accidentally misrepresented the demo flight thinking it was part of CRS, not COTS. My point is still correct though, that Antares by itself is much much less than $240m per flight.