Derelicts are easy made. Just fire on an ship with pilot until the sparks start flying of. This is the moment the pilot decides to abandon ship. The longer you keep the ship in this state the more likely it is the pilot will eject at last.I think partly it will depend on how often players come across, or can induce, a pilotless ship. If you can find one every other trip then the rewards should be towards the lower end of the scale.
To keep a ship in this state is difficult for a small ship. In most cases you kill it. But you can easy keep an anaconda or other heavy ship in this state. So if you go in salvaging you can create a derelict ship in most systems. That you rarely come across one is that pirates go for the final kill because they only want the cargo.
So if the payment gets to high, you can make money to easy. Payment should stay in balance with other ways of getting money, as Little Bear writes.