Amazon's doing a gold box deal on iPhone 6s's today, all around 20% off. The 64GB is $470 (20% off), the 128GB is $530 (18% off). I won't mention the 16GB, but a good deal if you don't mind refurbs.
https://www.amazon.com/Apple-iPhone-64GB-Unlocked-Smartphone/dp/B01CR1AA90
https://www.amazon.com/Apple-iPhone-64GB-Unlocked-Smartphone/dp/B01CR1AA90