Are you looking for costumes for next year? Or how about just to add to your costume collection? There are a bunch of costumes marked down to $1 at Walmart with $.97 shipping! Go HERE to take a look!
Old Navy will have all Halloween costumes and apparel on sale in-store only for just $2 on Friday & Saturday (10/30 & 31).
I imagine selection will be very limited, but it may even be a good opportunity to pick up bigger size costumes and themed-clothing for next year. Good luck!