How about sinking an oil tanker at the entrance to the Panama Canal? Anonymously, of course. We're not talking about a mentally stable guy here. He could do enough mischief with one or two anti-social acts to throw the economy of the western hemisphere into quite a tizzy.
Of course, he'd pay for it in spades. But never depend on a lunatic to pay much attention to the things that might deter a sane person.
You don’t need a sub to do that.
And sinking a tanker is not as easy as it sounds.
Besides, few tankers use the canal anymore. It’s too small.
As for buying submarines...let the jerk buy all he can afford. Each one is a Navy Cross waiting to happen for some deserving USN skipper.