If I were the one o either grant immunity or make deals, the FIRST person on my list would be Mueller, simply because he can get no substantial gain from it, other than his freedom by escaping jail or execution. Je has maxed out any time w]running the FBI, even got a waiver. The rest doesn't look good for him, appointment wise, and he will never go far in politics. So, he has little to gain, yet much to loose, by NOT cooperating. RR is right behind him, except I would make sure he either exited public service, or got severely reigned in.
Hate to break this to people, but money does NOT buy an election. If it did, Hillary would have won, since she outspent Trump near 2-1.