I can't speak to the science of mulch. I use coconut, and it suits me. I'm sure you probably saw this, but you can get 72 qts for 29.95 shipped. $.40 per qt vs $.60 per qt. 50% more to buy the smaller package.
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
It holds well, and your BP is going to live a long time.
I get that thirty bucks is thirty bucks, but long term the cost is less, and you don't have to worry about the effects on your snake.