You'd be lucky to find a decent home fo half a million. And than CoL is lower that in EU but still requires of 7 or 8k a month to have a good living.
But then lest get back to your original post, requiring 17 Million to allow a Thai retiree to settle in US isn't asking too much. It is a risk benefit ratio, half a million USD isn't much, so what if you let in an illegal worker, mafia member, etc ?
You see, admitting a young Thai with a good Masters degree and no money, is a much better deal than getting a Thai geezer with a modest bank account.