https://en.wikipedia.org/wiki/Single-room_occupancy
An SRO costs 25% as much to build as a studio apartment.
The real obvious solution is to take all of the money we are pumping into "long-term" affordable housing options into basically just dormitories. If it's good enough for college students, it should be good enough for anyone looking to get off the streets.
I think people really underrate how much of a knock-on affect there would be if we built enough SROs to meet demand. It would essentially establish a housing "floor" in any housing market, and undercut the ability to rent-seek up the rest of the housing market.
People have this mistaken idea that there are a ton of shipping containers that need to be recycled (there was a brief period in the mid aughts where this may have been true). But a used shipping container is neither cheap nor a great material to build a home from.
Yeah, see, this mindset is exactly the problem.
Letting anyone put a granny flat on their property if they have space for it is radical? Come on, that's a moderate change at most.
And yeah, that kind of thing is never going to make a big difference over the short or even medium term. You want a big impact quickly, you need bigger changes: allow for higher density "missing middle" housing across the whole city, drastically streamline the approval process to be "as of right", get rid of all mandatory parking minimums, invest tens of millions of tax dollars every year into new public housing, etc.