Bill Gates-backed startup can store carbon underground in plant-based bricks

$100 per ton, so:

"To get the atmosphere back to where it was before humans began to burn fossil fuels en masse would mean catching and storing more than 900 billion tons.

Today’s approaches can capture only a tiny fraction of what’s needed: around 2 billion tons of carbon dioxide annually, according to one recent study."^1

... so about $200 billion per year? That seems very reasonable. I imagine this would be a good use for old mines and things like that. What am I missing here?

[1] https://climate.mit.edu/ask-mit/how-much-carbon-dioxide-woul...