Charging for game design.

How much should i charge a client for designing an app for him?
I'm doing a few pages, maybe 4
icons and characters graphics, lots of elements for UI
and also the LOGO of the game.
What would be an appropriate price for this project done in 3 weeks?

Very interesting to know the answer, well it's been 3 weeks and now
I would like to know the more wealth you have now

congratulations

We haven't talked about it yet and the project is still going on. We are both students and he wouldn't be able to pay now. So I've decided to propose something like this.
Certain percentage of all the income through game download until the total of what I get reach a certain amount.
The amount and percentage would be decided(any suggestions?).
*income starts after the project is launched, plus I would be more than involved in future versions of game (I'm also learning Java to be able to develop my own games)