Can I check that online? How much money e.g. Stehen King or some other big name is making a year?
As Blessed Geek pointed out; writers are people, and you can't just go check their wages.
On the other hand; "famous writers" will likely have a net worth that can be found on the internet. For instance; Forbes: Stephen King's net worth (this from a Google search against the term
Stephen King net worth)
Keep in mind though that a net worth will include all assets they own, and any net worth they gain from other ventures and even from film rights and merchandise.
Literary authors don't have a regular income. They receive advances and royalties (a percentage of each individual book sale). Therefore, the monthly income varies with the author's productivity, the publisher's advances, and the numbers of readers buying his books.
Advances from indepentent publishers range between $1,000 and $5,000, while major publishers pay from $50,000 to $100,000. Alisa Valdes-Rodriguez received $475,000 for The Dirty Girls Social Club, Jonathan Safran Foer received $500,000 for the hardcover and $925,000 the paperback rights for his first novel, Everything Is Illuminated. (http://nymag.com/nymetro/news/media/features/n_8972/)
I don't know of a page collecting advances, but many of the higher ones have been reported in the news, so you should be able to find many with a Google search. For example Bill Clinton received $15 million and Pope John Paul II $8.5 million (http://www.thedailybeast.com/galleries/2012/10/04/lena-dunham-bill-clinton-keith-richards-more-big-book-deals-photos.html), but these are not authors in the regular sense and cannot be compared to the contracts of professional novel writers.