Can you correlate price with size of the phone? What about performance, weight, battery life and many other factors?
The Nexus 6 (184g, 31g/inch) is heavier than the Nexus 5 (130g, 26g/inch), compared to its screen size.
While the battery capacity of the Nexus 6 (3220 mAh) is significantly larger then the Nexus 5 (2300 mAh), people reported the battery life of the Nexus 6 to be shorter.
I can't find any technical improvement that could explain a 1.75x price increase.