I've posted this before but that is a meaningless statistic. You want to know how much is spent per person kept out of homelessness (or for some other services). Lets say we could spend an extra 10M to house the last 4999 of the hypothetical 5000 total homeless. Now we are spending an astronomical 10M per a single homeless person, clearly ludicrous but its simply that the metric is wrong. We are actually spending 2000 per person who isn't becoming homeless in this toy scenario, real life is obviously more complicated.

At the very least, buying all of them healthcare under ACA, although they might be eligible to get it subsidized.

Most homeless persons in California qualify for Medi-Cal. They run into other problems however, which the ACA premise wouldn't solve (only traditional universal healthcare would), so they get stuck using free clinics.

https://californiahealthline.org/morning-breakout/many-calif...

You don't even have to be here legally to receive MediCal (although those in SF would probably prefer Healthy SF).

That is a shame because it looks like Medi-Cal covers mental health services as well.

Or a basic income....

Would a basic income (often spoken of as about $12k/y) cover housing in the area they're currently frequenting? If not, what will that realistically change?