Generally the mass produced ones are cheap. Cheap in their manufacture, not in cost necessarily. The highest quality Neko-mimi hair bands are made by cosplayers themselves, its a matter of getting the proper materials, usually a fake fur of 2 colors, or even stuff like rabbit fur, with the proper support and mounting, are far beyond the mass manufactured items.
If you do not want to make them yourself, you may have to look for a pair to be imported, unless you live in japan and can navigate your way to a cosplay shop, or one of the anime culture shopping districts.