Luffy I think will hit 2 billion. I know people always say Luffy has to surpass the bounties of whoever he defeats, but I think at this stage, it's still too early for a 4 billion bounty, especially since that would mean surpassing Blackbeard, and I don't see that happening. I see Luffy and BB having relatively similar bounties by the time they finally clash.
Zoro and Sanji will be on or near a billion. Their bounties are laughably low considering their threat level, and compared to Luffy.
Jinbei should be just below whatever Zoro and Sanji get. I've always thought if we have to break up the Monster Trio (which I don't think Oda will), that Zoro, Sanji, and Jinbei would be the new M3, with Luffy a tier above them.
The others I'm not sure about, although I'd like to see Franky be well over 100 million. I don't like that he's so low, and Robin needs a huge boost. She should be right under Jinbei, imo.
Also, I don't know what number to pick, but I really, really want Chopper to get a proper bounty.