For all other iphones in the past Apple have made sure that all carriers are selling the handset at the same price.
The only thing that has ever differed between carriers is the amount of free minutes, texts and data you get.
The Price of the handset and the monthly cost has remained steady across the networks because apple fix the price and they take revenue from the monthly payment.
I cannot see why they would change this now for the new phone. So i am assuming the prices published by Orange will be the same across all carriers and the only thing that will differ will be the bundled mins texts and data.
Only my assumption mind !