For anyone who's still looking for a Halloween costume...here are some amazing options I came across:
HOLRAN costume
COSPA costume
The Holran one is actually the first one I saw. It looks really nice, and it's cheaper by far, but there have been some sizing issues reported for it. Not just that it runs smaller (since it uses the Asian sizing system, people from other countries may have to pick larger sizes than normal), but also in the skirt being too long or too tight, or similar issues with the top, etc.
The COSPA one has no such complaints, but only one review. It looks amazing, with the blazer capturing the original's shimmery effect, and comes with a plush headset. It costs 3-4 times as much, though. In the same ballpark as buying Miku herself.
Anyway, some nice window shopping, or maybe more than that if you feel like splurging. If I weren't a guy,
I'd wear these, and feel pretty cool doing it. :)