Turnil, looks like Timmundo might be your best bet so far, I doubt you will get any other offers than that. I by no means make a ton of money writing RPG stuff, I doubt I make as much as I spend on the hobby even in a good quarter, but that doesn't mean that I will jump at any chance I get to write something. I suspect that is true for others who do so. There are to many other things that have to be considered.
You are looking for someone to write a campaign setting for you, great. Where are you going to get the money to pay them? Now, I am not saying that you do not have the money nor that you would default on a contract after the work has been done, but if you are not intending for this to make a profit then as a potential writer I dont know if or how I am going to be paid.
As a potential employer it means, or would for me, that you are going to have to put something down up front, but thats a risk for you. In my, admitedly limited, experiance both publishers and writers disappear. Even when something gets published and sold and does well sometimes publishers dont get around to paying you when they are supposed to do so. Or you spend a lot of time writing something that gets hung up and never gets published in spite of good faith on your part and the publisher's. Sometimes its legitimate reasons and sometimes its not. Writers do the same thing, they promise and do not deliver.
Then there are all the complications of what the writer invisions versus what you invision for the product, and the question of pay compounds that.
Basically I am simply saying that what your asking for is going to be tricky. You might want to rethink your approach. If you are saying "I am willing to pay X for a game book, so why don't I just get someone to write one for me?" I understand your logic, but I advice caution.
What you want sounds pretty specific to me, far to specific for these conditions IMO. A better model might be to give a potential author a list of setting elements you want to incorporate, things that dont require an author to go out and read novels they may not be familiar with. At that point the author would submit a summary to you, say a 2-4 page proposal with an estimated total word count. If you like it then you would pay the author a small downpayment. The author would proceed, writing a single chapter of an approximate predetermined length and releasing it to you after payment. Perhaps the first chapter would be considered "paid" by the down payment. The author writes each chapter in an agreed upon time frame, and you pay for it based on what you have previously seen or perhaps 2-3 sample pages. If you dont like the last chapter you paid for you can either end the arangement and start over with someone else or ask for a rewrite. The author does the rewrite in hopes that you will buy future chapters. However, the author retains the right to refuse and end the contract as well. That way there is minimal investment on both sides up front. Allowing the author to retain publication rights and product identity would help keep an author interested.
PS IME people who get paid $s per word are more likely getting a lump sum based on the type rather than length of the article or are fulfilling a contract that works out to X per word, usually where what the magazine is really paying for is the research and legwork that goes into a relatively small article.