A OEM Nissan door shell (unpainted) is about $406 US from one of our sponsors. But be mindful of shipping charges... they can easily add a couple hundred to the cost:
https://www.everythingnissan.c...gid=0
You can also buy just the outer door skin/sheet metal, but IMHO it's not worth it as the labor to replace the skin may cost more than replacing the entire door.
Another alternative is find a used door at an auto recycler. Here is great site for searching recycled auto parts throughout the US and Canada:
http://car-part.com/
If you are lucky, you might find a pristine door in the same color. If not, a simple repaint is all that is required. Nice thing about used, is you save the expense of having to remove all the hardware from the old door and installing in a new door shell. Or worst case, you just have to swap simple stuff like the interior door panel.
Good luck!