Covert bribery is definitely frowned upon. Overt bribery - hiring lobbyists, event sponsorships, regulatory capture, etc - is very popular, I'd even say it's more so than in other countries.
Going through a few intermediaries, I don't see a reason why a presidential pardon in exchange for $100MM in crypto couldn't be arranged either, especially in the dying hours of a presidency.
Obviously this is all silly spy novel stuff, but a reasonably intelligent person with mid-level or better criminal connections and literally a billion dollars to work with, coupled with a hell of a lot of motivation, could probably figure out something.
All that being said, outside of real political backing (i.e. continual payments every month), I'd doubt the person would remain free for very long after the deal was done.
1B gets you in the door. You still need to know the right people to pay off. You can't just google it. This is why you see all the billionaires at their billionaire parties, good old networking.
https://en.wikipedia.org/wiki/Bill_Clinton_pardon_controvers... https://en.wikipedia.org/wiki/List_of_people_pardoned_by_Bil...
You should read Swiss investigative journalist, Daniel Amman’s King of Oil.
The furor over these pardons including the Marc Rich pardon was 100% political.
Clinton pardoned relatively the same amount of people as previous presidents but with a heavy focus on “leftists.”
Also, Marc Rich had left the US before he started working across trade embargoes and singlehandedly built the OTC oil market. He also worked actively with the US on covert oil sales while being prosecuted by the DOJ.
Trump tends to pardon the people who will get him into the news cycle, like sadistic war criminals, corrupt or openly racist officials like Blagojevich and Arpaio, or whoever Kim Kardashian told him to.