A home requires: pmi (possibly, often on jumbos) until 80% ltv; insurance, at $300-$350 per month per million dollars; taxes, at roughly $1k per month per million dollars; earthquake insurance, particularly if you're near a fault line; and maintenance, of which I'd budget $5k/year on a million dollar home. Maybe more for CAs housing stock. So that $6k becomes $4k for a mortgage.
Using a house for retirement savings is for idiots; that's an enormous gamble on the future of CA 35 years from now.
The Madison house, btw, is in a location walkable from many offices; Madison is more competent than the bay area, so while buses aren't great, the roads are very drivable in many directions. Someone with even an hour long round trip commute has a very long commute there (except, perhaps, after snowfall.) So you could probably use one car, or one commuter car and one beater car for a couple. Not two cars as you need on the peninsula or sf for a couple with kids.
Not to mention that $70k doesn't capture all the other things significantly cheaper in Madison: food, daycare, and education (many Madison schools are quite good) being the most important. Many peninsula schools are quite good, but not in sf.
Cost wise, I did ignore insurance costs, but yours needs to factor mortgage interest deduction. You might be getting income taxes reduced by $2k/month.
If you view it as plausible your house value will collapse, you shouldn't buy a house. If so, you'd rent and you'd be looking at much lower housing costs.
With regards to cost of living: some things are much more expensive in Madison; e.g. utilities (no A/C needed in Bay Area; heating rarely needed).
Using a house for retirement savings is for idiots; that's an enormous gamble on the future of CA 35 years from now.
The Madison house, btw, is in a location walkable from many offices; Madison is more competent than the bay area, so while buses aren't great, the roads are very drivable in many directions. Someone with even an hour long round trip commute has a very long commute there (except, perhaps, after snowfall.) So you could probably use one car, or one commuter car and one beater car for a couple. Not two cars as you need on the peninsula or sf for a couple with kids.
Not to mention that $70k doesn't capture all the other things significantly cheaper in Madison: food, daycare, and education (many Madison schools are quite good) being the most important. Many peninsula schools are quite good, but not in sf.