Perhaps you already know that iPhone does not cost same in all countries of the world.
If you are living in the United States, you can get an iPhone 5S at a price of $200 with a contract with the phone company. But if you want to buy iPhone 5S without a contract, you can get it $707 which also includes all taxes.
This is really not cheap but this is the cheapest you can get an iPhone in the world. In every other country, iPhone is pricier than this which is based on the data from Mobile Unlokced website.
The website also gives the iPhone price compared with the per capita GDP. You can see that if you buy an iPhone 5S, it is the highest percentage per capital income i .e 22.7% of GDP. This is just 1.37% in United States.