> How many condos do you have to build in the bay area to make it cheaper than Tracy ?
It doesn't necessarily need to be cheaper, but comparable when including transportation costs. And I think the answer for that would be, not very many, as a percentage of the land area.
By definition, if we took 1/10th of the already residential area of San Jose, and increased the density 10x, we'd be able to almost double the housing capacity (1.9x). That's not hard to do if we build 6-7 stories high and the entire surface area covered is housing without lawns and so on.
If our goal is a more modest 5x increase in density, which is easy with typical 4+1 story apartment builds, we could re-zone 10% of the residential area for that and capacity would be 1.4x what it is now. For a city like San Jose with a population of over 1,000,000, that means it could support a further 400,000 people.
We could also add some residential mini-skyscrapers in downtown Mountain View, Palo Alto, and other smaller cities, possibly with reduced parking, for people who want to live, work, and shop downtown.
According to Wikipedia, the 9-county "SF Bay Area" has a population of 7.76 million. If we remove San Francisco and Oakland from this, plus round that up to removing 2 million let's say for the areas that we can consider "sufficiently dense", that still means about 6 million people live in areas that are suburban-like and could be densified. By increasing density 5x in 10% of already residential areas of these cities by building upward, more than another 1,000,000 people could live in the Bay Area. And obviously we could apply this to 20-30-40% rather than just 10% to support much larger populations, and build slightly higher as well.