I have bought a number of things from shops in S E Asia. I looked online to see how much the same items cost.
The shops I bought from are shops which supply mechanics and bike shops, and are also open to the public. The shops are a bit like distributors, and a bit like retailers. It seems they just get in the cheapest products, which is what people here want. They don't have a large selection.
Item 1: Derailleur - made in China.
This derailleur is US$2.25 in the shop.
On Ebay it is normally US$10.20, but now discounted 5% to $9.69. Free shipping is included.
I did not find it on Amazon.
Item 2: Shimano Tourney derailleur. Probably not genuine Shimano.
In the shop, this is US$3.75.
On Ebay this is US$14.99, plus $5.99 postage, totalling $20.98.
On Amazon the same derailleur is not Shimano. It is $17.99. Shipping is extra, and how much depends on where you have it shipped to.
It is possible that two different companies make the same derailleur. It is more likely that none of them are made by Shimano.
It kind of makes sense. Shipping probably costs much more than manufacturing.
It would cost even more to buy the same items in a shop in the US or another country.