The craziest price I've seen so far is on O2 for an iPhone 7 Plus. You can get 50 GB of data, unlimited minutes and texts, Unlimited EU data roaming and music streaming and the yearly upgrade programme for £59.99 upfront and a staggering £95 a month! It's the most expensive plan I've seen yet across the four networks.
Looking at the flagship (iPhone 7 Plus 256 GB), the next most expensive is Three with all you can eat data, minutes and texts, 30 GB of personal hotspot and feel at home for £87 a month and no upfront cost. Then there's Vodafone at £73 a month, but this is for only 30 GB of data, but unlimited minutes and texts, unlimited roaming mins and texts and 4 GB of roaming data. I can't get on EE's store for over 20 minutes now as the site is so busy, but I think the most expensive was £70.99 a month for 40 GB of data on the 4GEE Max plan (unlimited calls and texts including EU roaming, 15 GB of roaming data and BT Sport).
It's also interesting to see how the plans are arrange. EE don't seem to be offering any essential plans on the new phone and the lowest data option on the 256 GB 7 Plus is 10 GB. I guess they think that those who what that phone will have lots of money and therefore the lower data options won't interest them. Surely it won't hurt to offer some slightly cheaper plans (although the upfront cost is normally huge on them so maybe that's why they haven't bothered). Also, I'm surprised to see no price reductions on the iPhone 6S and 6S Plus yet. Saying that, the 6 and 6 Plus and even the 5S is still on EE's website at the minute, and the price was about the same for 10 GB of data as what I'm paying now for my S7. Why would you pay so much for a three year old phone? I've only been looking at EE for the older phones so I can't comment on the other networks. They're probably just as bad for this.