In short, if a seller in Indonesia or mainland China offers to sell you one of anything at a price that is too good to be true, it's probably not going to be a genuine brand name item. At best, you're going to get a counterfeit. This goes for electronics, bikes, bike parts, anything. That price sounds ridiculously low, and Western Union? That's like dropping a bag of cash down a blind alley for a stranger. Zero consumer protection, zero ability to identify the person picking it up. If this person sends you nothing, you have no way of getting your money back or even reporting this person to authorities.
You can't manufacture something and sell it for less than a third of the usual retail price and make a profit. Another thing that looks odd is the fact that Shimano's own corporate site makes no mention of Indonesia, only Singapore.
Wire transfer isn't much better, especially if the receiving account is not a corporate account. There's nothing really definitive, but a lot that would make me suspicious.
If you're in Croatia, you can probably find a more local dealer. They seem to distribute merchandise there.
If you're unsure, you can also contact Shimano directly and find out where the best place would be to purchase parts. They would also, presumably, be able to tell you if that really is their manufacturer and whether they can legally sell direct.
for contact information and locations of dealers.