Most expensive betta fish species are undoubtedly the most difficult. In recent years, it has become the most expensive betta fish in the world due to the reduction of species with excessive and unconscious hunting. At the same time, the elegance of their tails is not in any other fish. The bettas are so valuable that one of them can reach thousands of dollars. That is why you can find normal bettas in pet stores, but rare bettas are even sold in auctions with auctions because they are very expensive. Like 1-10 Million Dollars!
Source: https://fishingrod-en.com/most-expensive-betta-fish/