In addition to the Lester assassinations, all I did was during legal trouble mission, I invested in FlyUS (I believe that's what it's called), which doubled my money and after the 3rd or 4th assassination I did hitchhiker random event (Tinkle)
You can probably end up with like 3+ billion doing it this way, I just spent a lot of money doing other stuff, surprised I even ended up with that much
The GoldCoast shares ended up giving me a solid billion + in profit alone, but that's because I invested like 1.5 billion into it
Oh so you just invensted a fuckload of money in flyus and blew up every single plane which belonged to the other company? ^^