Note that this is a mathematical model the authors present. It’s not data from the real world.

We estimated that the annual cost of housing would be $20 900 per person housed.

Their estimate of costs is much lower than the real-world cost of providing just a shelter bed (not permanent housing) in a large city. A shelter bed costs NYC about $50,000 per year. With that said, I have not looked at their sources for that number.

Edit: they’re also not including the cost of building housing.

Our analysis assumes that housing for PEH is available. Construction of new housing would be a substantial additional expense. The cost of affordable housing varies from $150 000 to $1 million per unit nationwide.

A 30 year mortgage to pay for the construction of a unit that costs the minimum $150,000 would cost about $16,000 per year. For a million dollar unit, such a mortgage would cost about $108,000 per year. (These are costs for an individual. Municipalities may get lower interest rates.)