I love using Kindle's as single purpose tablet/interfaces/displays. I'm the weirdo who actually prefers the LCD displays vs eInk and it's incredibly easy to set Kindle Fire's into dev mode which lets you display a webpage, never turn off while connected to power and never show ads.

You can regularly find the Kindle Fire HD10s for ~$40

Good to know about Kindle Fire. And hah, I can totally see why you'd prefer LCD's over e-ink - no ghosting + readable in pitch dark would be a sweet upgrade to the dashboard.