what should i charge?

Hey,
I hope posted this in right tread.
Anyways, I have a client who I'm doin this site for. Now when I'm done he wants to know how much I would charge to do Icons and graphics for the site whenever he needs.

I dunno wat to charge so can someone help me out here. His description is as stated. Just graphics and icon designs and text designs, etc for the page as he needs them or see fit for a page.

What would u advise me to charge?