iPhone SE 64GB on Vodafone, free upfront, Unlimited calls and texts, 3GB of data - £28 per month. £672 overall. (Mobiles.co.uk)
Use voucher code SE6465OFF to get the upfront cost lowered to FREE upfront instead of £65. £28 a month for 3GB of data and unlimited minutes/texts seems pretty good too. Link is for Space Grey. Other colours available too via links in comment below.