Let's imagine the bill of material is about $30, and that's cheap knowing they have mid to high end embedded SoCs or DSPs being able to move 4K video.
To that price, you also need to add a continuous software development for the OS and some apps (even if they are Open Source, because they need to do at least some modifications). Minor bugs will happen and you would need to solve them.
Also, more complex hardware and software usually equals more complex testing and debugging, and with this more person-hours and a bigger cost. At the end, it might not be $100, but it will be near enough to round it for $100.
To be clear, this is said without having ever worked in a TV manufacturing company, but knowing how this kind of things are made, I think I'm not too far from reality.
To that price, you also need to add a continuous software development for the OS and some apps (even if they are Open Source, because they need to do at least some modifications). Minor bugs will happen and you would need to solve them.
Also, more complex hardware and software usually equals more complex testing and debugging, and with this more person-hours and a bigger cost. At the end, it might not be $100, but it will be near enough to round it for $100.
To be clear, this is said without having ever worked in a TV manufacturing company, but knowing how this kind of things are made, I think I'm not too far from reality.