Read the statement by Michael Teeuw here.
What is the cheapest used monitor or cheapest monitor in general to use? I was looking at this one currently:
Seems like a good price. I was a bit worried about it being TN panel (they usually have very poor viewing angles), but the website lists it with 170 / 160 viewing angle. I think the colors will still be messed up at larger angles, but since MagicMirror is mostly black and white, it doesn’t matter so much.
Overall, I haven’t owned a TN panel in years, so I can’t give a certain answer.
EDIT: But then again, I don’t live in the USA, so maybe the prices are a bit lower there. 50 € for a used monitor is a quite okay price over here.