Re: the SD slot
It's not just the material cost here, it's the value Apple have attached to having more storage on the iPhone.
Current cost of an iPhone SE SIM-free on Carphone Warehouse:
16GB model - £359
64GB model - £439
iPhone 6S SIM-free:
16GB model - £529
64GB model - £599
Apple seem to attach a value of £70 to a 48GB memory upgrade - whereas a 64GB SanDisk MicroSD XC1 is £14.38* or a 128GB is £34.99** on Amazon.co.uk. So it's worth a lot more to them than simply losing 50p, they're actually losing £70.50 per phone that might have been upgraded, as 16GB is very restrictive in terms of what can be stored on the phone and is often regarded as just present in the price list so they can say the iPhone cost is "from" a particular price. This is the only thing that's good about the iPhone 7 as far as I can see - they've removed the 16GB option from the lineup.