The true cost of housing is relatively flat across the developed world and especially the US. The actual cost is almost entirely a function of local politics.
We could have a flood of nice, brand new homes for $300k in Silicon Valley and nice older homes for $200k, in the same way a city like Tokyo or Houston does, if the people of California had not made the deliberate choice to pull up the ladder behind them.
You won't have brand new homes in $300k in SV because the land itself is worth more than that due to the heavy demand for housing in what is a comparatively small area, though you might get $300k condos in multi-story buildings if the zoning issues in the Bay Area are addressed.
Houston isn't a good example either. Houston has almost no zoning or building regulations, which was on ample display when entire neighborhoods flooded because developers weren't prevented from building houses in flood basins. (CA allows the construction of residential properties in floodplains, which are flat areas that might get flooded if flood control mechanisms fail. In Houston, houses were built in the flood control mechanism.)
There are also plenty of places in California where houses and residential units are being built. In LA, for example, several ten thousands of new residential units were built in the downtown/downtown-adjacent units in the past few years. In San Bernardino/Riverside counties, they still have housing stock available from the last building boom. It's not that the people of California pulled that ladder up; it's simply basic market forces: too many people want to live in the nice parts of California.
We could have a flood of nice, brand new homes for $300k in Silicon Valley and nice older homes for $200k, in the same way a city like Tokyo or Houston does, if the people of California had not made the deliberate choice to pull up the ladder behind them.