“What’s great about the Internet is that everyone is on a level playing field. Due to the relatively cheap or free access to search engines you can compete with big websites with minimal investment on your part. You don’t need lots of money to run a popular profitable website, all you need is time and know-how, and the time requirement isn’t even that much. While some websites may require more maintenance than others a typical site can be managed in your spare time, in the evenings or on weekends.
As far as how much you can make? The sky’s the limit, however keep your head firmly planted on earth. It is possible to have a monthly income of a few hundred to a few thousand dollars off a website(s) you run in your spare time, that is an attainable goal. It is also possible to make much more than that, but expecting more is a less realistic goal. Don’t go into your website project with the expectation of millions of dollars, chances are it isn’t going to happen. However, if you are after supplemental income that will last residually for a long time (quite possibly the rest of your life), then this guide will tell you how to do it.
There are no miracles here or magic systems, you will need to follow the correct steps and you will need to work on things. Your first site might fail, your second one too, but maybe your third site will be the one to succeed. After I launched my first commercial site it took me a year and a half before I started making good money, and then another 8 months before I started making great money. There wasn’t anything magical about it when I finally became a successful self-employed website publisher. It was the result of work, sacrifice, and learning from my mistakes. I have taken everything I learned in my road to success and placed it here.”
From this Guide from Chris Beasley that offers a detailed, step by step explanation of how to build a successful (i.e. profitable) website.