The networks have always been a rip off and even more so this time round.
For an iPhone 6 Plus 128GB EE charges £149 upfront then £63.99 for 24 months which over the total life of the contract will set you back around £1,686. Add in my wife's iPhone 6 64GB EE charges for example £149 upfront then £45.99 for 24 months which will be around £1,253. That is a total spend of £2,939.
So from the Apple Store I have just purchased an iPhone 6 Plus 128GB and iPhone 6 64GB outright SIM free for around £1,400. With a SIM only contract from 3 Mobile for £15 each over 12 months, which I will probably extend to 24 then that is £30 * 24 = £720. So total spend is £2,120 which is a saving of £819. Those 3 Mobile SIM only deals give me all you can eat data, 200 mins (300 mins 3 to 3), unlimited texts, 4GB tethering, free 0800 calls and Feels At Home where in places like Italy, Australia and USA you can use your phone as you would at home and not worry about roaming costs (25GB limit on data abroad

). If you need more minutes, get the 4GB data and then you get 600 mins. Oh, and 3 also offers 4G for free. Plus I have been a 3 customer for the past 3 years and their network is the fastest and most reliable. Bit of an advert for 3, but great network.
If you cannot afford to buy a phone outright then your old phone should make up some of the difference (about £180 for an iPhone 5 in good condition on phone trade in websites) and Apple also have interest free credit available if you need to make up the difference.
Not only that if I did decide I wanted a change after 12 months to the S line or to Android then I could, or even after a few months I would probably get most of my money back for the iPhone.