Here is a list of stores where I shop, as well as some others, that are fairly inexpensive and have cool things to dress like a nerd.
H&M - I put this as number one because I work there and don’t want to be traitorous. It keeps up with trends and is definitely at the lower end of my price range.
Forever 21 - This is the cheapest place that I shop. Literally, almost everything is under $25 and they have a lot of cute stuff. It’s probably the best store to hit to try to put together any Potter outfits because it’s so cheap and they have SO much.
Another cheap place is Kohls.
Urban Outfitters & Free People - My two favorite places to shop! Free People is more expensive than Urban and at the very top of my price point, but everything is really nice and lasts forever. FP is more boho and hippie-ish, while Urban is more hipster, but I still love them both.
Sorry to all my followers from other countries that don’t have all of these stores :[