Illustrators range from the wildly successful to the wildly broke, so it's hard to give you an average income. We'll give you a few vague guidelines as far as salary is concerned, but just assume that you’ll either have to work part time and supplement it with a secondary job or else have to give up on it completely. It may not be the case, but it's a real possibility. Then, if you do have success, great! You can even write to us and rub it in our faces! We hope you do!
When first starting out, you'll be lucky if you crack $20k a year. Unless you can get hired by a company early on, you are more likely going to be building a portfolio by doing freelance work for various employers who are willing to take a chance on an untested new illustrator with no prior experience. True, it will depend a lot on whether or not they like what they see, but if you've never done any work for anyone else, they may wonder why that is.
Top illustrators may make as much as $80k a year (or even more, if they get uber-lucky), but don't count on ever hitting that mark in your lifetime. It isn't likely. You may be working for a company, which would mean steadier pay, but the money will be steadily low. If you are giving it a shot as an independent artist, you are really rolling the dice. You could hit the jackpot with a successful series of books or you could find yourself on food stamps.
Whatever you do, don't get your heart set on doing newspaper illustrations. Neither you—nor the newspaper—are likely to be up and running for very long.