I was thinking a Twilio style model. Sign up, account gets charged with a few dollars for testing. Then there would be a small fee per file, I was thinking $0

I was thinking a Twilio style model. Sign up, account gets charged with a few dollars for testing. Then there would be a small fee per file, I was thinking $0.05 to $0.10 per file, or a penny a page. Haven't really gotten that far with it. Edit: I should have also mentioned that I don't think this could be ad supported because the end user will likely never see anything but the output file, as it's an API and not a user facing service.