He used the same display from the old iPhone and replaced the cracked glass panel while making sure to keep the original Touch ID home button, which can't be replaced easily.
Touch ID home buttons are exclusively paired with the iPhone they came with. A new Touch ID home button wouldn't work with the parts from the original iPhone 8 Jeffreys bought from eBay. Only Apple can replace a Touch ID home button, as it has the software that's needed to pair the new Touch ID home button to an iPhone.
And after assembling everything together, he ended up with this:
The cost of the iPhone 8 from eBay and other parts he needed, like the housing and glass panel, came to a total of $390 AUS, which is about $278 USD.
Jeffreys did need to use specific tools from iFixit that cost $60 and weren't factored into the cost of restoring the iPhone. He also used a handy magnetic mat to keep all the screws and parts organized, which cost $20.
Assuming that most of us don't own a specialty toolkit from iFixit or a magnetic mat, the total cost of restoring the iPhone 8 is closer to $358. That's still just under $400 less than a brand new 256GB iPhone 8.
Buying a cheap damaged iPhone from eBay and restoring it seems like a great idea if you want an iPhone for much less than Apple sells it. But taking apart an iPhone and putting it back together is a pretty involved process — and not every damaged phone is damaged in the same way, so it could require more extensive repairs.
The bottom line: If you're planning on trying it out yourself for the first time, expect lots of trial and error, and potentially a totally non-functional iPhone.