I found this thing on amazon for $15. Please tell me that wasn't anywhere near the $40-50 range https://www.amazon.com/K-EXCLUSIVE-8-Bullwhip/dp/B073M83FJ3/ref=sr_1_9?s=sporting-goods&ie=UTF8&qid=1523737010&sr=1-9&keywords=bullwhip
https://www.amazon.com/gp/product/B07RKKF5D3/ref=ppx_yo_dt_b_asin_title_o08_s00?ie=UTF8&psc=1
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This is the one that I settled on. I tried 2 other weights before this one. Of the same brand I should add.
I'd actually recommend making a pipe whip (like some 1/2 in pvc and a coupler ~3 bucks of pvc) and about 1000 ft of paracord (~$40 if all black) and some fishing line for a cracker. I use 1000 ft because its cheaper for the volume you get, and allows you to overestimate how much cord you'll need for your whip. Sometimes I bind the core with dental floss, which is like 99c from the dollar store or free from your dentist :) I haven't tried out this paracord, but I use a similar 1000 ft roll from paracord planet Additionally, sometimes if I want my whips to pop visually, I can sink some extra money into glow in the dark cord or special colors for the final belly. Black is cheaper for the insides, and is a pretty color anyway.
I've seen leather whips with BB loaded paracord cores before. Might be something you could consider. Alternatively, I found this listing for 2.36mm lead shot on Amazon: https://www.amazon.com/dp/B01C51TD22?psc=1
I'm pretty sure it's this one...but I'm ordering soon...so don't own it yet. I left the book that recommended it in my car today...have to remember to bring it in to page through...
http://www.amazon.com/Braiding-Fine-Leather-Techniques-Australian/dp/0870335448