Any doubt modern publishing is big business? In 1975, the year’s best-selling book, E.L. Doctorow’s Ragtime sold 232,000. By 2000, John Grisham’s The Brethren exceeded the sales total of “Ragtime” by twelvefold. So what do the big-time authors make? A New York Magazine survey does the math: Tom Clancy gets $45 million for two books, which works out to an advance of $42,694 per page, or $133 per word. See what some of the others make…