Doesn't look terribly difficult.
Do you have any experience sewing? A pattern for that sort of dress should be easy enough to find. Seems like it would be a relatively simple beginner project for a novice seamstress.
Alternatively, it should be pretty easy to find a Halloween-themed dress that's very similar. My wife has one but I can't remember offhand where she got it - I'll see if I can find a picture of it when I get home.
I assume that the long parts of the bottom of the dress (left side of the second photo) is frayed/torn fabric - is that a shorter skirt underneath, or a liner of the outer dress?
A quick bit of googlin' brought me to this, which should be a pretty close base piece for you to modify: