You do not even know what I need done, therefore you can not make that assumption!
Unless your costume is a simple belt or something equally non-complicated and -massive, waiting until the beginning of October to commission something pretty much guarantees that you'll not be getting your commission until well after Halloween. And even then, your maker won't appreciate a rush job - consider that he or she has to get size and construction information from you, possibly to include design sketches, firm up design and correct any design flaws, acquire materials, actually make the thing, and ship it (the last of which requires at least a week, and that might not be long enough, depending on what's being sent). You're leaving a mere 4 weeks, and making the unfounded assumption that whoever you contact has literally NOTHING ELSE TO DO, either on commission for someone else or simply for his or her own benefit. Just think about that - if you want a replica-grade costume for Halloween, start planning it in the spring and commission it by summer at the latest. Quality isn't just expensive - it takes TIME. Thus endeth the lesson, and the dogpile. :cool
If you want an off-the-shelf item, that might be something you could get in time. I see you're looking for a Jedi robe - I got a cotton-twill one a while back from Mystik Merchant, and am generally pleased with it. It hasn't softened up much yet (because I hardly ever wear it), so it's still pretty stiff and doesn't flow as well as I'd like, but construction is solid and high-quality. Looks like they don't do wool anymore, only a "mid-weight poly/cotton", but they advertise that they can get robes to you before Halloween. Order soon, though.