Wal-Mart or Spirit Halloween store are probably going to be your best bet for what you're looking for. Both are not costly, and carry a wide array of costumes. They should both have Vampries, Ghouls, Ghosts, and Trolls to tickle your fancy.
You can get great ideas for making scary customes at your local Michaels store or Party City. You can also go to the following websites such as familycrafts.com or www.costumepatterns.net
Well if you like pranks, get a scary costume (doesn't matter what it is) Have a friend to stay over for the night of Halloween and watch a scary movie. Have another person to wear the costume while you two are watching the movie. Tell your friend that you need something from the closet, the person openes the door and the person with the scary costume will scare the person. Simple as that.
If you are looking for unique costume ideas, you can find them at http://www.essortment.com/halloween-costume-ideas-50-unique-weird-ideas-52253.html. You can also find unique decorating ideas at http://www.halloween-website.com/decorating.htm
If you want costume ideas then the best place for that would be online on some Halloween websites. You can also just go to a website that has Audrey Hepburn costume ideas on their as well.
Family Fun Magazine offers some great Halloween costume ideas. They offer individual costume ideas or ideas you can use for the whole family! http://familyfun.go.com/crafts/ducks-662521/
This website: http://www.parents.com/holiday/halloween/costumes/ has some fun and unique costume ideas for your new born. But remember to dress them in a warm costume.
There are many non scary costume ideas for children. For girls, princesses, Disney characters, and angels are a few popular choices. For boys, superhero costumes are a good choice.
The websites Uproxx, Glamour, Petticoat Lane and Haunted in Hillsboro have multiple pages and lists dedicated to costume ideas for those who are on a budget.
Costume ideas can be found at Costume Supercenter or Anytime Costumes. Alternatively, one could search Google Images for the theme that one wished to dress as for inspiration.
You can find unique Halloween costume from website such as costumeideazone.com; costumeideazone.com/CIZ/CostumesByCategories.aspx?c=9; www.halloweencostumeideas.com
Just wear nothing and put on a mask.
Researching online is a great way to find unique costume ideas to suit your needs. I have found a great website for you that will give you several different ideas for halloween costumes. http://costumeideazone.com/