examples~ :3
Generally, I base my asking price on the prospective length of the story (in Microsoft word pages or the words themselves.) and the interest that I take in the story. If I'm interested, I don't charge as much because I'll actually enjoy writing it, haha.
So, if you let me know ABOUT how many pages you want, I can give you a price. The number you give is just a minimum, too. I may write over that if the inspiration should strike (: