50% are used parts sourced from Bookoo, Craigslist or Ebay.
The GPU price is low because I was gifted a GTX 980, which later I was able to sell for $400.00, with that I was able to partially fund a GTX 980ti. After about a week the card was having some issues with the fan, I immediately took it back to Micro Center and they offered a replacement, I informed them I had already activated one of the games (Bullets and Blades promotion) for a $60.00 value. They stated it was fine and that I could now activate the other game; which I did, then sent in for the $10.00 rebate. Unfortunately about 3 weeks ago the 980ti died, and I sent it to EVGA for an RMA, it had about 3 months left on the warranty and they sent me the 1080. 5 days before the warranty ended for the 1080, EVGA replaced it with a 1080ti.. I cannot overstate how lucky I have felt using their products.
So how I see it is $689.00-$530 = $159.00