Wait for it my friend your the one thats gonna need your head checked.
£200-£250 would be a good price.
are you bipolar?
£250 is around $350 US. i'm sure you can find an iPhone for around there on the market in your area. then you won't have to sign a contract and you'll have a cheap plan.
oh and your mockup is ugly. thank god you don't work for Apple.