Does Apple charge for changing dialogs, popups and menus?

Question

iOS

I suggest the client to change pop-up windows: pop-ups, the style of backgrounds in application sections. He claims that in Android the style of windows changes without problems, while iOS requires thousands of dollars to make changes in application windows. The essence of the style change is to make everything in the same style, and so that the windows do not differ from the application. For clarification, I sketched below.
1. What is the difficulty in changing native styles to custom ones?
2. How difficult is it for a developer to implement?
3. Do I need to make any payment to change the styles and how much does it cost?
Thanks for the replies.

Answer 1

1 and 2 -> it is difficult for someone, not difficult for someone, each performer has his own assessment of what is difficult and what is not.
3 -> it costs as much as the performer asks for (no more, no less), it has only an indirect relationship to complexity (the price depends on the market).