If you want to get a grip of what writing can pay, have a look at the NUJ rates at:
http://www.londonfreelance.org/rates/index.htm l and this offers updated rates for books, mags, features etc. Click each section for rates.
The WAYB is a good source of reference for contcats and info about publishers - if you submit manuscripts (MS) there are certain recommended guidelines like only send a synopsis, not the whole book, the MS should ideally be double spaced, do enclose an SAE if you want it back, and do not be put off by rejections.
Probably every author gets rejection after rejection before landing a deal - and the deal could be for �100 to start with by the way, so don't plan the move to the country just yet perhaps..
On the whole though, plenty of people do make a living at writing and if you are thinking of getting published, do have a shot. And do not self publish by the way - vanity publishing is all but ignored for any but the most vain writers and the titles are virtually never stocked by any book shop, library or book club. Just not worth it. And do get your MS vetted by someone who is not a friend who will be objective, not just saying its good to make you feel chuffed. . .
Loads of good info on the web as well for writers, so good luck . .