Ok, longtime lurker here. Just thought i'd post some bounty thoughts.
Luffy
550,000,000 for defeating doflamingo, ceasar clown and oneshotting a pacafista
Zoro
240,000,000 for his showing against the pacifista and strength according to tashigi
Sanji
180,000,000 for his showing against the pacifista and standing up to vergo, according to tashigi
Franky
144,000,000 for blowing up vegapunk's lab, his showing against baby5/buffalo and his very public fights this arc. His bounty should rise fastest early because he uniquely cannot get stronger, so it should rise quickly then plateau
Robin
110,000,000 just for being visible
Brook
77,000,000 for being the famous soul king, bounty upgrade for being a strawhat
Usopp
100,000,000 he was super visible this arc
Nami
40,000,000 just cuz
Chopper
100…nobody has a clue about him
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Jimbei
410,000,000 will join after new bounties
Kinemon
75,000,000 Visible in punk hazard and is somehow important in the next arc (zou)