If you take away their data mining and advertising revenue, you’re going to need to pay extra. Especially if you’re in a high end market segment (humongous TV) where there’s little demand for a dumb TV outside the digital signage industry (which tends to demand higher standards because those things are always on).
The cheapest and easiest workaround is to get one of those Google TVs that has the ability to switch back to “basic TV” mode. That way you can get a TV from the consumer segment, subsided by other people’s use of smart features.
You could also DIY a dumb TV by getting a compatible TV, ripping out the internals (don’t kill yourself by shorting out the power supply!), and replacing them with an HDMI controller board from sites like AliExpress.