I definitely wasn't planning to base pricing on what users were submitting or how frequently they were using the app. I was initially thinking of selling to businesses rather than individual consumers, and enterprise pricing is pretty variable -- based on factors like head count, which categories (e.g., 'accountants', 'doctors') would be useful, etc. Hence the flexible pricing model. If there's enough interest among individual users though -- which there seems to be -- I'd be happy to offer a basic tier that's transparent.