There are two categories of technologies that tend to land in that price range. There are things that cause existing rocks to react with CO2 faster (such as crushing olivine), and there are ones that use a combination of electricity and catalysts / reversible chemical reactions to either concentrate the CO2 or cause it to fix to some abundant chemical.

They are all quite pie in the sky in the sense that they're mostly startups with no operational experience in large scale chemical manufacturing trying to build up plants (and organizations to build the plants) from scratch.

However, at least some of them rely on bog-standard chemistry, and the chemistry only requires chemical reactions that we already perform at industrial scale.

I get the distinct impression that if US said it was going to federalize any oil company that still had net CO2 emissions in 2028 (and also suspend any patents in this space as part of an emergency action), the logistics would magically work themselves out. I'd guess it would only cost a few weeks of oil industry profits (so, ~ $10B) total to prove out a half dozen technologies. At that point, many copies of the top two or three plants could be replicated out globally.