Apple has a store in India:

https://www.apple.com/in/iphone/

iPhone 13 is listed as ₹69900.00 (920$) vs. $799 in the USA. The former includes taxes, so its only fair to add $80 to the latter (taxes in my state are 10%), so it is still around $40 difference, which isn't bad.

But it appears that the iPhone 13s sold in India today are already being produced in India. If that is the case, any secondary resalers on Amazon are going to take a loss if they imported the phones the hard way (though they could have just smuggled them in).