Cheapest and easiest way of doing this:
Hire Ma "The Pillar" Mixer. Its a new class, fixer. You can now hire two people who hate each other.
Then hire Hugh "Tank" Miller
and then Gibby Millard.
Last two hate each other then it pops. You can hire in a different order but Ma "The Pillar" Mixer can not be last.
You need 150 notoriety to hire Gibby Millard, the rest are super early/ Total cost is 12 k. You can easily speed run a new game and get this or take a save early in your main game and get this very quickly then reload and carry on.
Other mixes are available, but this is the cheapest ive found a fixer and two people that hate each other. Remember the hate has to go both ways or it wont op. Hate is shown by a red line on the gangster recruitment screen and it MUST goes both ways.