For those that don't know, check out the mission NPCs once in a while. You can negotiate the price/rewards and sometimes get 3 X what is listed. Managed to get 4 Ionised Gas for killing scavengers at a settlement. Easy peasy missiles from ship. Takes 30 seconds to kill them once there.
If you aren't in particular good odour with the faction offering the mission, you frequently get a big fat middle finger. There are risks inherent in greed (FDev, I'm looking at you).