I've made several since buying the one for Sparky.
The plastic "pony" beads are strung on a wire and fed through a length of plastic tubing. The ends are capped with large plastic beads, a bell is attached to the bottom and a small length of chain to the top for hanging. (The clip to hang the boing is a normal pear clip or link clip)
The boing is then wound spirally to create the "loops" and Voila - finished.
The most difficult part was finding stainless steel wire in the correct gauge.
I insisted on using stainless steel wire as that metal is the safest for use with our budgies, even though the only place you actually have exposed wire is at the two ends.
You could use 14 gauge wire (which is about 1.6 mm)
but I'd probably go for 12 gauge (which is about 2 mm)
I used 18 gauge (about 1 mm) which ended up not having the tensile strength necessary for maintaining a taut spiral when completed.
The arthritis in my hands prevents me from making addition ones at this time but with the right gauge wire, the toys are awesome and I like them much better than the rope boings.
I bought the plastic pony beads from Michaels Crafts, the plastic tubing from Home Depot, the large end beads and stainless steel wire were purchased on-line.