Closet Child: link
(This link is for ordering internationally. They are a Japan-based used clothing shop for brand-name alternative clothing.)
Getting around the site is a lot easier if you can read at least a little Japanese, but it's still manageable if not.
Not EVERYTHING will be under $100; prices vary based on the brand, the item, and the item's condition. But it's definitely cheaper than a lot of places.
It will be cheaper to buy plain base clothes and then buy accessories you can add on yourself like cheap costume jewellery and bow (whatever you're style)you could even add iron on patterns etc.