A little lesson in econ. That coral is worth whatever you and the seller agree on. Sure do the research and get some ideas, but it comes down to - is the amount of money on the coral or something else, or rather have the money in my pocket than in the tank. If you are happy to get the coral and he is happy to get the money it was a fair price.
Next, when comparing the cost of corals on Java Island to the US we need to know how hard it is to get $5 in Java and $60 in the US. A starting point might be what is the minimum wage in Java or average per capita income.