in UK it's almost unfathomable to be paying anything for the phone if you are getting a contract
Here's EE's page for a 16GB iPhone 5s. Prices range from 9.99 to 149.99 depending on the plan chosen:
http://shop.ee.co.uk/mobile-phones/pay-monthly/iphone-5s-16g...
Look at the next model up, 32GB, and the up-front cost increases significantly:
http://shop.ee.co.uk/mobile-phones/pay-monthly/iphone-5s-32g...