SJSinNYC,
I prefaced my comment by noting that there is CY Similac formula available, it’s just more expensive. I know people who were told to use treif formula in cases where the infant couldn’t tolerate kosher ones, so I would agree that if no other formula was available, chalav stam would certainly be better! But there are definitely poskim who aren’t matir chalav stam simply for expense. (When I wrote under any circumstances, I didn’t mean even pikuach nefesh.)
mbachur,
If the chalav stam is free, that would certainly constitute grounds to be meikil according to R’ Moshe.
For those who consider CY a chumra, but do keep it, I think it’s a good question, whether one should use soy based formula instead of milk based formula, to avoid CS.