About a fortnight ago I bought a second hand Samyang 14mm F/2.8 off of Gumtree for $350 and it works quite well. Many of the Samyang/Rokinon lens' have at least one aspherical element which makes them very good for their price range for astro work - better coma control generally.
It had first light about two weeks ago.
http://www.astrobin.com/301682/
Samyang have also just released a 14mm F/2.4 (think that's correct) which apparently controls the coma considerably better and has less distortion.