If you can live with manual focus, just get the Rokinon 85 1.4. You could probably get it in the US for about 299$. It's just superb, covers FX and is sharp at 1.4. If you must, you could sell the 18-105, but if it was me I wouldn't. Who knows when you will need the 18mm...
Good luck with your choice.
Good luck with your choice.