If it is not a high resolution camera, the cam itself only costs ~1$. That's more than enough for a camera module to scan QR codes.
The batteries are not included i'd guess. And the connectors for the battery are like a few cents.
The hardware cost of the device is definitely way below 10$.
Make it for $10 bucks, mybe you get rich.
We can also make a bet and see who will predict correct price for this device.
Trezor is also cheap to make, but they sell it for higher value because they want to make profit and not charity.