I need some Graphic Design for IOS and Android App.

We are looking to hire a designer to create the graphics that are to be included in a App that we are working on. The App will be for iPhone, iPad, Android Smart Phones and also Android tablets also FAQ and Tutorial website that supports the app. The current App designers have figured on creating these graphics themselves but I thought that I should inquire as to what it would cost to relieve them of this task and to allow them to concentrate on the function of the app itself.