I might start doing this, but I could use some suggestions and advice from others who do story commissions. Mostly around how to charge and so on, but any advice from you is welcome.
Everyone seems to charge at some sort of basis, whether it's per page, per thousand words, or per 500 words. It really depends on your preference. I like to charge by page myself, at about $4 per, which I think is also what my buddy
As for charging, the way I do it is by estimates. I come up with an estimate of how much it will be, invoice them for that amount, and then I'll either refund or ask for more depending on the difference in the final product. Because I still believe that as artists, we should take upfront payment of some kind, even though writing isn't as easy to predict costs effectively, because it's filled by inspiration of plot devices rather than creative thinking of visual elements.
I believe it's better to at least take half of what you think it'll cost, because if you wait until the end product is finished, you run the risk of being cheated out of hours of work for nothing, unless it so happens you lock the file as read-only and password protect it so your client can't edit it or anything. Conversely, if you tell a client that you can put their idea into 10 pages, if you lock yourself in that constraint for the sake of not needing to refund or create a second bill, you have to sacrifice some detail that you may really want to add. Otherwise you're just creating additional pages for free.
Now, if a client says they only have so much they can pay for, like saying they can get an 8-page story, then you're already in effect locked in unless you're feeling generous. But it shouldn't become a constant, otherwise people may take advantage of your creativity to get a 15-page story but only pay for 12, or however it ends up being. Make sure you get your effort accounted for.
Everyone seems to charge at some sort of basis, whether it's per page, per thousand words, or per 50
