What to wear to homecoming?

My school's theme for homecoming is "What Used To Be Cool", so basically we're supposed to wear either 60's, 70's, or 80's stuff. I was thinking I'd go as a sort of seventies hippie with a hippie dress, a leather headband, and flowers in my hair. I need to find a cute hippie dress, preferably one I could wear again. Also it needs to be available in the Portland, OR area. Any ideas? Thank you!