But this is where you are incorrect. I have been given bounties after the wanted ship I have just killed has blown up. I did not get the bounty for killing the wanted criminal, I got the bounty from a fed NPC which has just attacked me after I killed the bountied NPC. I have used the Warrant scanner and waited until after scan before killing wanted criminals and have still received a 200 credit wanted bounty upon me. Lucky for me I jump to the nearest Friendly station and pay fine.
No point dying over 200 credits
Never once have a received a bounty on my head for killing a wanted ship, unless:
-The ship is only wanted in another jurisdiction (only the KWS will show that but won't say where they're wanted until you kill them) unless in an anarchy system, the ship is essentially "clean" as far as the authorities are concerned.
-I jump the gun on my scan (the automatic one) and shoot prior to it saying "wanted" in the lower left of the screen.
It sounds like your getting a bounty for getting shot BY authority ships after you kill a bounty if I understand correctly. If that's the case, it's definitely a bug. So it's not that I'm incorrect, it's that I've never experienced a bug that you have, which is surprising for me since all I do is bounty hunt in empire space or try to get my wanted status as high as I can in federation space. I'd ticket it if I were you. Unless the 200cr bounty is from returning fire on the fed ship, but from the way you post, it doesn't sound like that's the case.
Another factor could just be you shooting at someone who's the same faction as the authority ships. It's possible, but since you hunt in green (friendly) zones, it doesn't seem likely unless you shoot wanted ships that start as green to you.
As for dying over 200cr, the value isn't the point. The point is you shot another ship. It could be 1cr or 10,000cr for that offence, the value is not relevant. It isn't up to the criminal to decide if the laws are fair, it's up to the society. As such, society (FDev and in game authority) have decided that simply shooting another ship is grounds for death. You either play by the rules (don't do anything to get a bounty and watch your fire) or deal with the consequence. If the devs wanted it to be harder to get wanted, they could've simply made it so we get a fine for shooting another ship instead of a bounty. This could've been done in alpha before I signed on as a backer but the fact of the matter is, it's this way because FDev made it this way.
They've been pretty upfront on a number of occasions by saying something like, 'this is our game, we're making it how WE want. If you don't like it, you can go make your own game how YOU want."
EDIT: if or when FDev decides to change this, they will. Until that point, there's no sense whining about it. Just deal with it and learn the game mechanics as they are. If it too hard for people, they need to practise more.