

I thought I could see piles of debris at the bottoms of some slopes in the after pictures which weren’t there in the before pictures, but now that I’m looking at them again, I’m no longer sure that what I’m seeing isn’t just a difference in the shadows. (Presumably the pictures were taken at different times of the day.) I’m going to edit my original statement.
Note that this is a mathematical model the authors present. It’s not data from the real world.
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.
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.)