Luffy has never beaten an opponent and gotten a lower bounty than them. Not with Alvida, Buggy, Don Krieg, Arlong, Crocodile, Moriah, Doflamingo, Cracker or Katakuri. Bounties are kinda pointless, apart from hyping up characters. Once Luffy takes down a Yonko, there is no point in keeping his bounty to 3 billion. His bounty will triple to 5 billion, like it always does. He wasn't as strong as any of the Warlords he beat either, but his bounty was higher.
As for the Shichibukai these are my guesses
Mihawk: Frozen = 700 mill to 1 billion. Updated = 2 billion on the dot.
Doflamingo (as"Joker"): 1.5 billion.
Doflamingo (now, if escaped): 1 billion.
Hancock: Updated = 500 million to 800 million.
Weevil: Updated = 500 million to 800 million.
Crocodile: Updated = 450 million.
Moriah: Updated = 400 million.
I know :p but since I gave everyone else, felt fck it and gave Doffy as well...lolz. With regards to Doffy's bounty, I flirted with the idea of 1,340,000,000 and I reckon given his influence he could have a figure like that but given Katakuri was that next big step for Luffy after beating Doffy, couldn't bring myself to do it...lolz
Luffy stood 0% chance in a 1 v. 1 against Doflamingo. 'Mingo was a raid boss. Katakuri was to Doflamingo what Rob Lucci was to Crocodile. Blueno was Cracker. The only difference is that Luffy got his powerup (FS) at the end, not at the beginning of the arc (G2/G3). Luffy took down
2 opponents, not 1.
Dressrosa -> Alabasta (1st Warlord)
Zou -> Skypeia (Island in the sky)
WCI -> Ennies Lobby (Escape arc, where Luffy takes down 2 people Lucci/Blueno, Katakuri/Cracker)
Reverie -> Water 7 (Garp hyping up Yonko, Dragon vs. WG, Weapons of Mass Destruction, etc...)
Thriller Bark -> Wano (Fought Kaido's rival, Ryuma, Wano, Captain John with Rox, mentions of Big Mom, etc...)
You know what's funny about this? Queen is 1,320,000,000 and a lot of people are guessing King is going to be 1,330,000,000 based on Zoro/Sanji. So you'd have Joker at 1,340,000,000.