I dunno.
The city of Los Angeles had access to land and planning resources and they still arrived at optimal cost of $350,000 per barebones unit http://www.latimes.com/local/california/la-me-ln-prop-hhh-qa...
As the linked article politely notes, those costs are likely to overrun once the construction starts "A Times analysis of projects funded by the California Tax Credit Allocation Committee, which includes most permanent supportive housing projects, shows that recent projects have usually cost more, averaging about $420,000 per unit in 2016."
Even if land is semi-free or government-owned, the zoning has been taken care of and the architectural designs are obtained pro bono, it still costs money to get building materials, hire labor, provide parking spaces, develop infrastructure and build the residences on a code-compliant way.
And let's just say that $420,000 a head goes a long way in many non-coastal areas of the United States.
This would have been easily doable. Hell if the political will were there building that many units in a year would be feasible.
But you can't zone that, you can't mandate it. You can't grant easements; you can't even used condemned public property.
Because our political system has been captured by greedy bastards like Vhinod Khosla and Donald Trump.