And that cost falls squarely on the site owner not the comment service. Moderation may be as expensive or as cheap as you make it.

Big Tech is spending a lot of money on it, thousands of people and jobs and algorithms.

If you ask me, it's a fools errand and I hope that they waste their money trying to build a clean Internet.

Reference: https://www.remarkbox.com/remarkbox-is-now-pay-what-you-can....

I don’t know the rules for Disqus but I expect that they impose at least some limits to block bots and spam, which is almost impossible to achieve for a small site.

Check out akismet, it works for wordpress and is likely all you need to divide spam from ham during moderation.