Hello!
First of all let me introduce myself. My name is Marko and I've been a freelance 3D modeler/animator for over a year now, I've mostly been working with indie studios on games and the characters in games. I've also written my bachelors thesis on facial animation. As I do not have enough info for a good estimation how much this would cost, I'm going to provide my estimated hourly rate which is 12-15 USD/HR.
Well I guess that's enough about me, so lets talk about your project.
What type of game is it? - shooter, horror, survival?
What do you need to be written? enemy AI, character movement, user interface ...?
Do you already have all the assets?
When do you plan to launch?
Do you already have the level and mechanics designed?
As you can see there are a lot of open questions that need answers. Feel free to contact me so we can discuss your project further and find the best solution for you.
Best regards,
Marko