A replacement should be half the price. I think the origional covers the admin/checks they have to do. They don't need to do these for a replacement one though. I suppose the govenment are after all they can get at the moment though .
We're off to Paris in the summer so I've got mine and ds's to pay for. £8 for pictures, £7 for a replacement birth certificate for ds as I keep loosing them , then the passports, hotel etc. They shouldn't be so bloody expensive!