If you want a factory unlocked smartphone with a USA warranty and GSM compatibility AND like the idea of having optional add-on modules (like the Hasselblad True Zoom camera), the Motorola Moto Z smartphone is on sale for $500 with free shipping at B&H Photo (with free B&H photo/video kit), and by Amazon itself.
On the other hand, if you want to pay a lot less AND want a phone that works with all four major US carriers, B&H Photo is offering the new condition 64GB Moto G4 PLUS with a free B&H photo/video kit for $220 with free shipping. This is available in black or white. The 64GB version also has 4GB of RAM, while the 16GB version has 2GB of RAM, so keep that in mind.
UPDATE: speaking of smartphones, the brand new HTC U11 with its 12mp Ultrapixels and a 90 DXoMark score is now available for pre-order at Amazon by Amazon itself.