I recently switched back to AT&T from Verizon because they introduced a new plan called the Mobile Share Value plan that offers non-subsidized pricing if you own your phone. There are two rates for each line on this plan. If you own your phone the rate is $15/month for the line. If you buy a "contract price" phone that rate is $40/month for the line and you have a 2 year contract.
In case you didn't get that, they will charge you and extra $25/month for 2 years to pay for the rest of that phone. Over 24 months that ends up being $600.
With that, here are the actual iPhone 6 Plus costs:
iPhone 6 Plus 16GB: $899
iPhone 6 Plus 64GB: $999
iPhone 6 Plus 128GB: $1099
iPhone 6 Plus 16GB: $749
iPhone 6 Plus 64GB: $849
iPhone 6 Plus 128GB: $949
The other thing to consider is with non-contract plans you don't have a 2 year contract. I know that seems obvious but let me just say it once again... you don't have a 2 year contract. You are free to terminate your service any time you want with no cancellation fees.