Ive been looking for a decent enough deal for a Nexus 6 for a while. All contracts with reasonable data use seem to be around the £40 mark - personally I'm a high data user, so 10gb suits me, but there are other deals with auto cashback on the same site which are also eligible for the £42 cash back.
Motorola Google Nexus 6 32gb
On EE Double Speed 4G
No upfront cost
£65 auto cashback - £65.00 will be credited directly into your bank account 90 days from connection. There is no need to claim and they will email you to let you know when the money is on its way.
£42 potential cashback via topcashback.
With the cashback this works out as £39.51 per month.