I don’t think anyone but the daftest people think that Japan costs 1/100th of what the US does.

Living in Japan with a Japanese lifestyle is not that expensive. I have many Japanese friends living in Tokyo for under $1.5-2k a month. They’re not living in luxury, but they quite enjoy their lives, travel every once in a while, etc. You won’t be doing that in SF (and Tokyo is a much more pleasant city than SF in more ways than one).

On the other hand, living an american lifestyle in Japan (big car, big house, eating lots of red meat, buying imported American goods, etc) is going to cost you a lot of money though.