On average in San Diego, it will cost about $500k for an existing house with land or about $200k for land plus $300k for a new house to be built on it: either way it’s a pretty steep climb for many of us.
Wondering why you can’t find an affordable home to buy in San Diego? This article explains many of the forces at play. There aren’t a lot of easy answers. I’m glad they touch on ADUs / Granny Flats as one part of the solution.