The Snapdragon 820-powered Sony Xperia XZs launched in the US back in April this year, carrying a $699 price tag. But currently, you can get the device for as low as $399.99. Amazon has the handset listed for that price.
Officially, the phone is also available through a couple of other third-party retailers, but they are offering the XZs in $500-$550 range. So purchasing from Amazon will save you at-least $100. No information on when this discount ends.