Mainly you find cheap cosplays on e-bay. They won't be a good quality, especcially the wigs and if you want better quality then it is best to go up in the price margins.
This is what I found, you can have a try on cosplayshow.com a good website for cosplay costumes
You might be able to find some on ebay, or check out lightinthebox.com. (They're currently on sale!!)
You can try the shop in the related link.
Here is nice shop: http://www.cosplaydeal.com
You can probably find a cheap one on ebay.com. Alot of people sell the costumes for cheap prices, unlike the cosplay sites, whose costumes cost around a hundred dollars or so. I have not looked for pre-shippuuden Gaara costumes on ebay, but I have looked up pre-shippuuden and shippuuden costumes for Naruto and Sasuke, as well as Orochimaru, and have found the lowest cost to be around twenty-one dollars or so.
I don't believe that there are much stores that sell Final Fantasy 10 cosplay costumes, so your best bet would to be checking online. Online stores have great selections of Final Fantasy cosplay costumes.
CosplayMagic.com has a variety of costumes including the school girl costumes - see link .
There are tons and tons of different cosplay shops online. I've linked to them below.
Your local michaels or Joannes are good bets.
I know cosplay locator makes crazy custom stuff like that. But be prepared to pay out the wazoo.
== == == == == == == == Google Directory Cosplay http://www.google.com/Top/Arts/Animation/Anime/Fandom/Cosplay/ Anime Costume resources: http://anime.about.com/od/cosplay/tp/aa12.htm
Most cosplay stores sell mortal kombat cosplay.