I'm not sure I understand the criteria. He'd like to move into DC, but DC is too expensive. So he devises a filter that spits out (among a small number of other optimal locales) the Mission and Russian Hill in San Francisco. Both are among the most expensive places to live in the country.
For that matter, optimizing mostly for walkability, the filter spits out Lakeview in Chicago. But Lakeview is one of the most expensive neighborhoods in Chicago, and isn't significantly more walkable than many cheaper neighborhoods here.