3.000 Billion - Luffy
1.600 Billion - Zoro
1.377 Billion or 1.507 Billion - Sanji
Luffy's bounty would be a clean double.
Zoro's bounty would be more than King's bounty of 1.39 bil and Luffy's current 1.5 bil. His newer bounties consistently surpass Luffy's past ones. It's a 5x increase, and it's a clean number that befits his current feats.
I don't think Sanji deserves 1.507 bil, but he might get something like that. It would be more than Queen's bounty of 1.32 bil and Luffy's current. From his previous bounties, I derived 507 from adding 330 and 177.
Depending on if ZKK happens or not, Zoro's could be much larger than 1.6 billion.