Adding my response to be productive though, I bought a Mrs. Lovett apron at the Sweeney Todd revival a few years back with her pie shop logo and a bloody handprint on it, and have used it the past few years.
Wizard of Oz/Wicked seems to be the go-to group costume idea. It's well understood, creative to pull off and generally fun. Although, I'd think some retro 80's clothes could also be cool to use as RENT characters.
"Are you sorry for civilization? I am sorry for it too." ~Coast of Utopia: Shipwreck