Going by eBay, a lot of people are still managing to sell stolen iPhones for $100-$300: http://www.ebay.com/sch/i.html?_nkw=icl0ud%20locked&LH_Compl...
New screens are pretty cheap these days; under $40 for a new iPhone 6 screen wholesale currently. Used batteries are worth nothing since new batteries are so cheap (a new 6 battery is less than $10 -- why would you want a used one?) Camera, home button, charge port, prox sensor...even if you put all those together you'd barely have $100 worth of parts, and that's talking about new part prices (wholesale).