Sustainable affordability is achieved at the balance of supply and demand.

Supply can only be increased by building upward and outward: increase density near jobs, and invest in effective regional public transportation to mitigate "Manhattanization" (extreme density) or "Los Angeleization" (car commuting hell).

Demand grows from increased economic prospects, so can be managed with progressive taxes (ideally reinvested in transit/education/job training that equalize economic opportunities).

Subsidized housing makes sense as an interim solution, a buffer as the market adapts, but those subsidies are ultimately unsustainable (requiring prescient central planning).