The potential cost of missing players and a damaged season would dwarf that. I can't imagine that 43 million is an amount they'd balk at to reduce the risk.
The 'benefit' for vaccinated players seems more likely to me, but that isn't something the NFL wants.. that's something they've giving up because the players want it.
That's why I tend to see this a PR move from Tretter. I don't think he has the players on board with it.