As mentioned you can travel to a opposing faction and "undermine" by interdicting and killing npc's marked hostile for 30 merits a pop.
This will count as murder so you will get a 6000cr bounty per kill, but that's no problem really, just pick a system you have no other use for and never dock in that system you will never get stuck with the bill.
Any ship could probably do this but a viper or diamondback scout would be my suggestion if you don't have all that much cash, and even if you do no need to risk a 12 mil rebuy on your pimped out python when a Diamondback will do
Hey I'm Thor -
People call me Bob.
Rule 1: Pillage. Then burn.
Rule 2: No such thing as overkill, as long as there are reloads.