There are a lot of false assumptions in this thread.
There is no set amount of mobs you need to kill, nor amount of time, nor amount of ped spent, to see a balanced return.
It is really simple: The more mobs you kill, the more likely you are to arrive close to / at your expected return, with current setup, skills etc. (be it 75% or 100%)
What you really have to do to be successful in this game, is find opportunities. People tend to liken this game to either slots or poker, and while there are aspects of this game that is similar to both those things (e.g. the pseudorandom payouts from slots or the parimutuel wagering of poker) I'd be more inclined to say that this game is more like chess than either of those two. Your job, to be successful is not to find the "right mob" to get the big fat hof. Your job is to analyze the moves that the game makes, analyze the moves that your opponents make, and try to capitalize on their misplays.
If someone more skilled than you, with better equipment is hunting a mob, maybe you should not go hunt that particular mob, because your opponent will be able to provide loot at a lower cost than you and still retain a better position financially.
Your job is not to copy what the seemingly successful people are doing. Your job is to find your own way, cause they're likely better than you at doing what they are doing successfully.. If you try to do the same, you end up losing to those people, one way or another. (fringe cases excluded)
In short, figure out how to make the most of the money that you spend, Also, shit happens:
only 0.01 are based on proper testing, proper numbers and facts stated by MA. Someone should start collecting this in a thread
That's a great idea!