I built a like-new(but really refurbished) iPhone 6S 16GB entirely from parts I bought in the public cell phone parts markets in Huaqiangbei. And it works!
How much did it cost? Answer here: https://youtu.be/-KucQDXnKws
I've been fascinated by the cell phone parts markets in Shenzhen, China for a while. I'd walked through them a bunch of times, but I still didn't understand basic things, like how they were organized or who was buying all these parts and what they were doing with them.
So when someone mentioned they wondered if you could build a working smartphone from parts in the markets, I jumped at the chance to really dive in and understand how everything works. Well, I sat on it for nine months, and then I dove in.