How to install HUD Projector on a 2017 Prius 2? I saw an amazon product for $50

Hello and welcome to the forum. AFAIK, cheap ones (circa $50) generally reflecta cell phone screen onto the windshield. The are seldom bright enough for daylight use, particularly in bright sunlight! If you can let us know the model and Amazon reference we could have a look see, but personally, I doubt it's usefulness. The better ones cost hundreds BTW as I'm sure you realize.