Total cost and steps involved with the process depend on the state of your design but usually involve me looking at any existing design, asking questions for potential designs and drafting initial ideas and concepts for your game.
Afterwards, I will refine your design once again based upon feedback and discussion with you and any others. Finally, it will conclude with me providing you a comprehensive, but easy to follow document with your games design (or the aspects of the design we agree to work on together).