The cost per click is dependent on an ad with a high CTR, in addition to a low cost per thousand impressions. Reddit ads, as mentioned in the post for example, are one place with low priced ad inventory.
You pay reddit per impression, not per click. Getting an ad that works out to $0.02 per click is not as easy as it sounds, especially if you're just trying to make them buy something on Amazon. Clickbait doesn't lead to sales very much, and advertising to capture attention of people who'd actually buy it leads to a very high cost per click.