I am doing research on this and so far am finding that the most accurate answer to this is: "Depends--It's negotiable."
However, that answer is not limited to traditional publishers at all! In fact, my experiences with the POD (print on demand) and "Self-publishing" services, seem even more likely and well known to vary of their costs and your cut.
However, there are general practices that I can outline about traditional Christian publishers that will give you an idea of what you can expect.
Typically, if a publisher approaches you with a contract, they will offer you an advance (money up front)and this amount can widely vary. I've heard a new author quote me $2000 and one who was on her sixth book quote me $5000 for an advance. The publisher is hoping that the book will sell enough copies to cover those costs, obviously. And, in fact, an "advance" means just that in that each book that sells the author contracts to receive a portion of the sale. Again, that varies, but I've heard often that amount could be 50 to 80 cents a book. Let's say the author is hot stuff and so they are able to contract for $1.00 a book, for easy figuring. So, if the publishing house has advanced $5000 to the author, the author must wait until the publishing house has sold 5000 copies of the book (to reimburse the publisher for the advance at $1 a book) before the author receives another dime for their book. From then on the author would receive $1 a book--this is for a book that sells in the stores for $12-$14, for example.
Before you run the publishing industry out of town on a rail, consider that the publisher is likely to spend $25,000 to promote that first book of yours. And by the way, they expect you to be out there signing books and speaking at every retreat you can to sell books as well. This is why, as one publisher took the time to tell me, publishers are no longer buying books, they are buying authors--authors who can turn out three to six books a year.
Since the American public is likely, after finding a book they like, to look for another book by the same author, there is much less of a risk, in the publishing house mindset, to publish someone with a following than a new author. Regardless of how good that new author's first book, the publisher just doesn't want the expense of introducing her to the public. Frustrating?
Wait. There's more. (And I promise in future bogs to cover viable alternatives to traditional publishing.)