Thrift stores are your friend. I've found many awesome things that I've used for cosplay in thrift stores. Also, don't overlook coats that are a little too big. A lot of the time, things can be taken in to fit your proportions.
'Idiot's Lantern' Rose Tyler (Doctor Who)
Astrid (How to Train Your Dragon)
Tinkerbell (Peter Pan)
Reviving This Year:
Annabeth Chase (Percy Jackson)
Katniss Everdeen (Hunger Games)