Doubt that Sabo got anything much higher than 2b.
What Luffy, Law and Kid have done was much bigger than what the Revos have done.
By defeating BM and Kaido they have totally broke the balance of the world, as now its basically a run for the One Piece, that is the real key to defeat the WG.
While the murder of Cobra, attacking Marijoa and clashing with admirals is a big PR boost for the Revos, its not as close the the impact that the fall of two Emperors, and the awakening of Nika, have in the world.
We have to remember that the New World is the real deal for the Throne, events on the Blues and the Paradise of course have repercutions, but nothing close to what happens in the NW, as there's is the place where those who could threat the WG are.
For Dragon, would be good to have more clarification on what "most wanted man" mean, as i have seen diferent translations that dont say anything about wanted, just that he is the "world biggest/worst criminal" and gives a doubt that his bounty will be the biggest one, i believe he will have something close to 5b, but not yet as high, as i belive only WB, Roger, Teach and Luffy will break the 5b.
For Mihawk, a good way to know his bounty is to imagine Zoro final one, as It probably will be a little above his master, i believe in something around 2.5b.