What is Berry in one piece?

In the One Piece anime and manga, Berry (or Belly) refers to the currency used in the world. It’s a type of currency made from gold, and it’s commonly used across various islands in the Grand Line and other parts of the One Piece world. The value of One Piece Berry varies depending on the location and the economic situation of each island.

What is the correct romanization of 'Berry' & 'Beli'?

It's pretty much the same as with "Horo"/"Holo". So the correct romanization would be either " Beri " or " Beli ". "Berry" probably appeared because "beri" sounds similar to "berry", and "berry" is an actual English world, or maybe there was another reason. As for the prices, looper's answer already mentions some of them . To compare the prices:

What is Luffy's bounty in one piece?

The Navy just give large bounties for pirates, Buggy has a 15 million bounty and Luffy has a 30 million. Would Luffy's bounty be an equivalent to 30 million Yen? What would be the real world value of the currency used in One Piece? Additional to the other answers, its symbol is: ! Beli symbol (grabbed from the One Piece wiki)