To be fair, NSF grants for pure mathematicians were never as substantial as for applied sciences, but they would routinely reach 500k–1M territory. That's the amount going to a single proposal, and grant panels in, say, analysis would definitely spend millions per application season. NSF funding data is public and can be looked up.

I'm using past tense because iirc NSF has recently reduced their funding volumes, although I'm not following the situation very closely.

NSF by itself contributes $200-300M a year towards math grants. Universities spend a billion+. Add corporate funding and other sources (DoD, other government agencies, private foundations) and you’re easily looking at a few billion dollars a year just in the US going to mathematicians.