Where is the best places to find halloween costumes?
This question is an illustration of how important the question itself is and how it is written.
If one is indeed fully committed to this act, then putting together a Halloween costume will become one of those 'journeys': first things first, it begins with an idea in your head before you ever set foot in a store, and then based on this vision and your infinite Resourcefulness, you will figure out for your self which resources (friends, stores, etc.) in town have the esoteric pieces you need.
Punchline: the simplicity of the approach of locating a 'place to find your halloween costume' circumvents the complex nature of this quest, that is, the journey inward.
Not really sure where you live so I can't reccomend any shops to you but you could try and customize an outfit out of some old clothes if buying them would be too expensive, I used to do it when I didn't have enough money to buy them : ) You could still buy some cheap accessories depending on what your going as, like fake blood if your going as a vampire or a simple witches hat. Hope this helps : ]