What about making it so you earn more money if the player you kill have specific permission, also that that player loses the same amount that you get by killing him.

So if I three ranks like this;

LowRank

• perm pvpreward.low (modifier 0.5)
  NormalRank
• perm pvpreward.normal (modifier 1.0)
  HighRank
• perm pvpreward.high (modifier 1.5)

So basically if there is new players on the server the old players will not earn that much on killing them and highrank players that normally have good gear gives a big reward if killed. Also if you get killed as a high rank you will also loose more money than a low rank.