The Navy actually doesn't determine bounty based entirely on power, but they also base it on how badly they want the particular guy caught.
Considering how DonFlamingo's bontybounty was 340 million beli, and he was a pretty big deal, It appears that the marines start leveling out the bounties around the 300-400 millionsmillion range.
That taken into account, If the admirals were pirates, their bounties would likely be in the 300 millionsmillion range.
As far as power goes (and power is not that quantifiable in one piece) They're, they're all in the top league, and so far, the only character who was formally introduced who can be said to have a very clear advantage over the admirals is Whitebeard, and He'she's dead.
the Other Yonko are very likely to be stronger than any particular admiral, but that's not necessaralynecessarily a concrete rule, and we yet to have a good measure of their power.