Oh for sure the volumes have a huge impact on price...but as you say, not necessarily quality!
That TV should have cost you 10x what a GTI would. That's probably an understatement... 100x maybe. Each one contains somewhere in the region of 12 million transistors, more than most high end microprocessors do, and each one has to function adequately. These things have features of the order of ~10nm and are made up of hundreds of patterned layers stacked each on the other. To set up the production line will have cost somewhere in the region of $1billion, and probably a similar amount in R&D effort before hand.
They often sell these things at a loss just to get the line running. An initial run of an LED screen Sony made was sold with a $1000 loss on each unit. They had to make them to learn how to make them and to get publicity anyway, but no way they could be sold for a profit.
I want to ask what make, but given this is a car forum I feel I'm getting off topic. I personally stay away from Samsung, but that said Samsung actually make a lot of the screens for Sony (who then double the price because they have better software to reproduce colours). Panasonic are a small player but are my current favourite. Quality is about 5x the Samsung level, but you'll pay about 50% more for it.
Ok, will try to stay on topic now. I wonder who makes the Discover Nav Pro screens for VW? That would be interesting to know.