$9 billion per year does sound like a bargain to fix homelessness, but I think it's unfortunately a lot more complicated than that. The poverty line for a single person in the US in 2019 is $12,490 per year, and there are roughly 40 million living in poverty (25 million adults and 15 million children). You'd be offering all these people (and more who are just above the line) a significant increase in income if they call themselves homeless. While it might still be a good idea to do this, you are now looking at numbers closer to $0.5-1 trillion, so it's a very different discussion.