For Halloween Costumes, Walmart is my first choice for the kids costumes. If you purchase early you have some very good ones to choose from. Walmart being as popular as it is for shopping, usually everything is cleaned out within a couple of weeks before Halloween.
To make sure your child gets the costume their heart is set on, shop Walmart but do it early.
Walmart has very good prices on their costumes and they meet the industry's safety standards when it comes to content, visibility, etc. That is very important when considering a costume for a little one.