>That only works if the system is closed. If housing in the bay area goes down in price, you get people moving in from New York, LA, Boston, Austin
If that were true the bay area would have been empty long ago because of the ridiculous housing cost. Fact is most people won't change cities for lower housing cost.
>The reason housing in the bay area is so high has nothing to do with fixed material costs or else housing everywhere would be that astronomical. The reason housing is so high is because demand is high and the supply of land is limited. Land is the primary costs. You fight that by building vertically. The higher the building, the lower the marginal cost of land for each unit and therefore things become more affordable. But like I said in my first post, this doesn't happen if everything is left up to the market because it isn't the way to be most profitable, so the government would need to be involved to incentivize this.
Developers are putting 5 on 1 buildings every where they possibly can because it's the most economically efficient use of the land. They can't in the bay area because of zoning restrictions. Remove the zoning restrictions and you'd see skyrocketing density.