With all of that in mind, I made a quick sketch of something that would be quick to produce in quantity and (hopefully) meet the criteria. The idea was for a bib style necklace made of strings of gathered squares.
I made a prototype using some cheap fabric from my stash. I cut 2.5 inch squares on the bias and stitched them together diagonally using basting stitches, then gathered.
Each necklace had three tiers (strings of squares) with varying amounts of squares. The tiers are arranged with the least amount (shortest string) at the top and the biggest at the bottom.
As a final touch, I attached the ends of the tiers to a strip of fabric, long enough to allow a head to go through.
All the band members wore black, letting the Bib Necklaces be the focus of the costume.