One thing to clarify is that, because some (~$60 Million in 2015 [3]) goes to housing assistance. The people helped by the budget includes more than 7,539 represented by the point in time count, so the $31K/person number is a bit high.
That said, SF spends a lot of money on homeless and the homeless population hasn't significantly decreased in over a decade.
[3] http://sfbos.org/sites/default/files/FileCenter/Documents/56... page 6