Fabric and ribbbon! - plus scissors, thread, and embroidery needles if possible. You could get lots of fabric remnants, or a couple yards of sale fabric; ribbon is often 5 for $1, a pack of embroidery needles ("real" needles but not as likely to prick as sharps!) can be split up, and you can probably get scissors and sewing kits at a dollar store.
No tech, something they might never have had access to, and something protected kids will perceive as dangerous (needles and scissors!), and as cheap as you want to make it.