Depends.
Fenexo makes as much as he does because CoC and TiTS have some kinks you won't find in many places.
He also built up a fan base over the years. He's active on his blog and forums which got his players involved and more people started writing scenes and his community took off, you don't see that much anywhere else.
People see that 30k+ a month he makes and think they can hit that but it took him quite some time.
Some other games like Lilith's Throne take off because the writing is good.
You also get outrunners pop up like Wanton Cove, Academy of Fetishes and E-Wardrobe that grab a few people.
It's all down to what you write about and how you do it.
There is a market for anything and everything if it's done well. Do it well and they will come, do it badly and they won't.
You have made 1 critical error though, you have put the money before the product. As it stands right at this moment in time, you are a nobody, you have no track record, no proof you can deliver a finished game and no fan base. Thinking anybody will pay is the last thing you want to be thinking about, getting people interested should come first.
Fenexo took years to get to where he is, some other text based devs haven't been around as long nor have that kind of player base and earn barely a fraction of the money.
This isn't the get rich quick industry it was when it was niche. There are only so many patrons and far more competition. Before thinking about how much to charge think about how to get people playing.
In other words, sort your priorities because you won't earn shit for months.