PSA: Don't buy the OnePlus 5 via Amazon (US)10
Right now, the US version of the OnePlus 5 - warranty included - can be found on Amazon for the insane prices of $779 (64 GB model), or $899 (128 GB model). The phone's international variant - without US warranty - is cheaper, but still more expensive than it should be: $559 (64 GB), or $639 (128 GB).
Obviously, you're better off if you're waiting until June 27, when the OnePlus 5 will be available directly from OnePlus' US website, warranty included. The smartphone's official prices are $479 (64 GB) and $539 (128 GB).