As a dog owner, I have stepped in a lot of dog shit — rarely from my own dogs. Properly disposing of your dog’s poop is a responsibility that goes along with owning a dog.
Dog poop doesn’t just mess up your footwear, it is a health hazard for people and other animals.
Why spend that kind of money on something you’re going to need a lot of?
I recommend what I use — the cheapest fold-over sandwich bags you can find. You can buy a box of 300-count store-brand baggies for a couple dollars.
If you have a large dog, plastic shopping bags work great. They have the added advantage of being free. I am sure your friends and family would be more than happy to pass on their accumulations if you have a shortage.