What's crazy is that he's only spending less than 1% of what the tax would cost him.
If he spent $10b and managed to save himself a $13b tax bill, he'd still save $3b.
I suspect he's actually spending much more than $100m. He has probably hired expensive attorneys, expensive accountants, expensive PR firms, etc. We have to hope he hasn't hired private detectives, hackers, hit men, etc.