20k at 4.3m assumes a really low mortgage rate. Current rates are at 7%+.

$3m home. 1.44% tax rate. 7.2% mortgage 20% down. $6k/yr insurance.

=> $20k/month

The numbers are mostly made up. As I am seeing stats say the average is 7.4% for jumbo loans and insurance is really about your own risk tolerance and what you can get away with in terms of minimum coverage. Tax rate will be variable based upon your super specific plot. Could be close to 1% - could be closer to 1.5%. Zillow says 1.44% for my neighbors homes. Some estimates were saying insurance was saying $1k/month but I've seen much lower in the bay but then again - depends on how close you are to trees, hills, etc.

But I can tell you that none of the homes near me have been selling below $3m. $3m is the floor.