literary/tv/film characters I would be:

• Margot Tenenbaum
• Angela Chase
• Marla Singer
• Junie B. Jones (lol such a literary figure)
• Hermione Granger
• Breakfast Club characters (group) (or other John Hughes' group)
• Princess Mia
• Kiki
• Olive from Easy A
• Sailor Moon

other options:

• the ever reliable cat option
• Zelda or Navi (w/ someone as Link)
• Rosie the Riveter
• B Spears circa "Baby One More Time" vid
• Catholic school girl! hahahaha. no.
• Greek goddess
• "homemade" superhero
• batgirl (group with other superheroes?)
• Spice Girls-group

costumes i wouldn't have to spend any money on (or hardly any):

• cat
  • cat ears, black outfit, eyeliner, tail (maybe $ on cloth)
• Olive from Easy A
  • red felt, top (sure that's easy to find)
• Hogwarts student
  • sweater, tie, black skirt, docs, tights, knee socks, SPEW pin, DH earrings