Honestly for anyone to be able to give you a ballpark figure they need to know what all will be included/necessary for the completion of the project.

1) Main Menu
2) In-Game Menu's
3) Etc. GUI
4) Level Design
5) Physics Programming
6) Shader Programming (if any)
8) Deformation Programming
9) General Programming
10) Etc. in general

Just need to know what all will be involved to even make a guess at the cost.