I would like to point out that I only pay in USD, so there will be some exchange differences. But even considering that, for a single project, the highest that I have paid out was $4,750 negotiated flat fee for a 130,000 word project, the writer was paid for a few other service fees, but the base pricing was negotiated and offered by the writer based on the scope of the project. For this particular project, because of the circumstances, I added some additional fees which increased what the writer received in total.
If I paid out by the hour at $18.75/hr, with an expectation of a cost per word at $0.06/word, that would be 312.5 words per day or 2,500 words per 8 hour period. If I maintained that production expectation, the writer would be hired for 120 hours, and would receive $2,250 as a flat fee for a 37,500 word project. I don't consider that unfair.
Since DB would be producing the treatment and the story concept, there is no question about buying copyright from the writer, copyright is owned by DB from the get-go, so there is no need to factor that into a fee schedule. In this process I would literally be using the writer to flesh expand the content, they won't need to think about how the story will develop or any other factors. So, I would offer that much of the higher level skills surrounding creativity that an author would add to a book, are non-existant. Perhaps, there are alternative views here?