Theory Dragon's bounty is 5 555 555 555 berry

#1
In the anime they called him the most wanted man. Not in the manga though. That lead many people to downplay Dragon's bounty. He wasn't literally called the most wanted man but it was heavily hinted at. The chapter that he is called "worst criminal" is also the chapter where the Four Emperors are introduced.
So Garp tells Luffy that his friend Shanks is a big deal in the New World, he is actually a dangerous Pirate, one of the Four Emperors. No big reaction from the crowd. Then Garp reveals that Luffy also has a relationship with Dragon, and everyone flips out. Dragon frightens people more than the Emperors.

Most wanted man is not such a unreasonable adaption if you keep in mind the whole context. The Four Empeors are called the greatest pirates. We later found out that those greatest pirates also had the highest bounties among pirates. Based on that, it makes sense to assume that the worst criminal also has the highest bounty among all criminals. Pirates are a subset of criminals, so Dragon should have a higher bounty then the Emperors.

The Emperor with the highest bounty back then was Whitebeard. He had a little more than 5b. Dragon won't have a higher bounty than Luffy's final one. Luffy will of course overcome his father in notoriety. His final bounty will probably be 5.6b, because 56 means Gomu and is a little higher than Roger's. So Dragon's bounty is between 5.1 and 5.6.

Why exactly 5.555.555.555? Oda keeps connecting Dragon to the number 5, which means Go. Here are FIVE examples:
Dragon has five regional Commanders (South Blue, West Blue, North Blue, East Blue, Grandline)
Dragon is from GOa Kingdom.
Dragon then set up his HQ in BaltiGO
Dragon was born on october the 5th
Dragon is 55 years old
 
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