What specific policies should I be demanding of our politicians to make housing affordable again?

The answer is Georgism combined with no zoning, but people aren't ready to hear about that yet.

By Georgism I mean a very high tax (80+%) on the unimproved value of land. It prevents land speculation and returns the value of the land to the public. Houses would be incredibly cheap, because you couldn't make money by merely owning land. The only reason to own a house would be to live in it, or to provide a true service for people who would actually prefer to rent.