After having the supplies for this for
Here's my finished product - 30 elastic hair ties for under $5:
I'll leave you to Bri's tutorial for the instructions, with one note from my own experience - I didn't try out the sizing of mine at the beginning (uhh, dumb), so mine are a leeeeeetle bit tight (they just barely fit over my hair 3 times), but I'm alright with that since these things tend to stretch out the more you use them. In any case, YMMV, so test out the size before you go cutting all of your elastic strips.
Thanks for the awesome idea and how-to, Bri! :)