Are they really that expensive? I looked up the device that I probably would want, and that would be the 55 inch 4k TV. Searching for a place to buy it revealed this link, that gives a price: https://www.uk.insight.com/en-gb/productinfo/lcd-tvs-and-dis...
It seems pretty reasonable to me. Is there a catch with that device that makes it not appropriate to use as your main TV?