but not everyone wants/is capable of buying a 150lb NEC tv made to resist vandalism and such, they just want a flimsy plastic panel that takes hdmi from their laptop and pushes it to an appreciably large 1080p panel

I just had look on Amazon and there are 42 inch dumb TVs available for about $220. A 32" one is $175

I just looked at amazon and a 42" monitor is about $500 (for a decent quality one). Where do you find these "dumb TVs"?

https://amzn.eu/d/7A6vnjn - if I search for "non smart TV" on Amazon it's the second link. The first is ironically a £1000 smart OLED.

The question really is, is it affordable? And how long before even that option disappears?

It won't disappear because it's a different market. A digital signage display is a large computer monitor. It has a remote, and typically also an RS232 interface to communicate what is pressed on the remote (as an alternative to HDMI CEC).