The next step to take after perusing through your closet is to check second hand stores. remember when going to these to keep an open mind. you may not find exactly what you were looking for, but you might find something that will work just as well, if not better. also, you may find a piece that will work, but is too big. If you can sew, altering the article won't be uch of a problem, but if you can not, try finding something else, or see if you can safty pin the article ofclothing to fit you. If the piece you find is too small, use common sense and look for something else.
The next place to look for supplies is some place like Wal-Mart or K-Mart, or Spencers. You can also try some places that specialize in costumes, but these wil be expensive. If you are doing a costume that requires face painting or wigs, a place like any of these is the best to look, but a place that does not specialize in costuming will only sell such items seasonaly. This is one reason why i stock up on face paint during the Halloween season. However, craft stores such as Ben Franklin's sell face paints like the ones used at fairs by clowns to paint children's faces year round.
If you are making a costume using a pattern (in short,if you are sewing), remember that the dollar table at Wal-Mart is your friend. Sometimes, you can find some treasures of cloth on the cheap tables. Try to stay as inexpensive as possible, but remember that sometimes, you may have to give and take when building a costume. If you can't find what you want for cheap, you may have to either (a) spend more or (b) not get exactly what you wanted for your costume. Please remember, though, that not everything works for all costumes. if you are planning to dress as Sally the Rag Doll, you probably will not want to wear neon orange and fabric with ballet shoes printed on it. Keep your materials realistic to your character/costume.
I hope this breifing was a help to any who read it. If you have any further questions of comments, I encourage you to email me. Please type "costuming" in the subject of your email or I may not reply.