Why am i not surprised that the Revolutionary Army Commanders are not near Yonko Commanders. There was debate that even though Sabo was the number 2 of the Revos, he only has the lowest bounty because he is the youngest and newest member. Now it looks like Sabo's 600 million bounty is the second highest the Revos got, not counting its leader Dragon himself.
As for Marco and Izo, i'm gonna guess that Marco must be below 1.5 billion, because Bao Huang did say that Luffy was the one that had the highest bounty on the enemies' side.
And Izo is around Ace's level huh? Interesting.