Like a few have mentioned you can decided on each project it self. From what i have seen $100.00 per page is average sometime's more depend's how good you are also!
Just estimate how long it will take you in hours, then add on a bit more since if you are like me you will always underestimate the time required then multiply by how much an hour of your time is worth.
This is an area I used to be nervous about, but once you can back up your skills with great work, you should charge what you feel is enough, after all it is your living!