Well last Halloween I went as the Female Main Character, Kimiko. And the costume was rather easy to assemble. I had to make the black jacket that the girls wear but otherwise I was able to assemble the costume from store bought items.
I'm pretty sure I can assemble the costume from mostly store bought items. The shirt might be a bit hard to find, but otherwise it should be easy. Much easier than the other costume I have planned. I might have them both finished by DragonCon, though.
Well, I'm mostly doing it because the Space Marines are the epitome of badassery, and I've always wanted to be one.
Also, the Ultramarines are my chapter. Every 40k game I play, I play Ultramarines if possible.
As for the movie, as I said in another thread (Ravenstein's, maybe?) I have mixed feelings. I'm trying not to let myself get excited lest it be a sh*tpile. But I WILL wear that costume to the first showing, yes.