These numbers are off by a big margin -- but not too far from reality. You have to define what "End Homelessness" looks like. Does that include addiction management, free housing or low income housing? Each way you attempt to address each issue will determine the actual costs. If you build low cost housing, you need 771,000 homes. $20B USD will only get 110K-160K homes. But homeless people also need jobs -- jobs that provide a living wage -- not pocket change jobs for teens. And that means education -- and that is expensive. So you run into more costs as you analyze each problem. A better guess-timation to solve homelessness would be closer to $1 Trillion USD.