Came here to say this. The production of a plastic bag costs somewhere in the range of 0.05 cents to produce. If you would factor in the impact on the environment it would probably cost a few cents. Which, given the insane amount of plastic bags that are consumed each day. Would be significant.
I think still less than a cent. I mean you just put plastic bag in a garbage pile, and that's it. Near-zero utilization costs with near-zero impact on the environment.
That consists to a great extent of maritime generated garbage - plastic fishing nets and plastic thrown off of vessels, and of course lots of "recycled" plastic that was being shipped to China and ended up dumped in the middle of the ocean.