RobertsDigital via eBay offers the Unlocked Apple iPhone 6 Plus 128GB Smartphone for GSM and CDMA Networks in Silver, Gold, or Space Grey, model no. A1524, for $909.99. Coupon code "CDTECH10" cuts it to $859.99. With free shipping, that's the lowest total price we could find by $39.

Note that the eBay page states the final price should be lower after applying the coupon; however, there is a $50 maximum discount with the coupon.