Thanks so much for all the suggestions!
I couldn't find the address for Sharihane until I checked posts today (probably better anyway, too tempting!), but yesterday I went to the Boulevard Barbes area that Meissoun mentioned and found a BEAUTIFUL Egyptian costume (gauntlets, skirt, bra all beaded) for under 200 euros--such a steal! I'll try to put up pictures of it some time
Here are the places I visited
Royal Spectacle (18 arr.)
Rue Livingstone
...this is where I bought my costume from; extremely helpful, not too pushy, a good selection from the basic 15 euro hip scarf to the 700 euro dream costume. Quality is good (nothing falling off of anything) and the prices can be negotiated a bit. In my costume-induced euphoria, I to get the business card, but it's right near many other dance shops in the 18th.
Fem'chic en Spectacle (18th arr.)
2, Rue Livingstone - 01 42 62 73 46
Also has a lot of other types of dance clothes...much pricier here, just about all of the nicer costumes cost at least 220 euros. Nice quality though, and extremely helpful saleswoman.
Au Decor de Paris (18th arr.)
11 Rue D'Orsel,
www.orselshow.com, 01 42 55 21 58
Tiny little shop, a good place for hip scarves and less fancy costumes
Hariri Baba (18th arr.)
5 Rue Pierre Picard, 06 17 14 12 49
Tiny store, absolutely crammed with stuff--expect to hunt here. Probably better for buying the basics (hip scarves, jewelery), as a lot of the sequins/beads were falling off of everything else.
Happy shopping, everyone, and thanks again for the advice