You're in a good spot to have a full time job you enjoy and (presumably) pays well. For me, the hardest part was building capital. I'd recommend saving every penny you can.
As for how to start, try lots of small things. Most of my ideas that worked took, at most, two weeks to test. Many started from writing an email or making a phone call.
There are countless niches now, full of people prepared to pay money. I chose LSAT prep. I'm sure already there's thing you know how to do that people will pay for. Some ways you can monetize that:
* An e-book guide to something, with free html articles as marketing for organic SEO and links
* Some useful tool people will link to. Serves as marketing for either ads, a product, or a paid version
* Videos on a topic. Can be marketing for any of the above, or lead to a paid video product.
"Start small, stay small" by Rob Walling is an excellent guide to bootstrapping a business. Possibly the best. It's aimed at software developers, but I was able to use it as a non-developer for guiding principles and marketing.
The Moz guide to SEO is a very useful intro to how SEO works. Essential reading if you're planning on going the free marketing route.
Lastly, the Four Hour Workweek is what got me started, and it's a great overview of the hacker mindset applied to business. For me, the idea was not "hehehe, how can I be lazy and work only 4 hours". It was "how can I make a business that can keep running even if I choose not to work on it". I do work quite a bit, but I don't HAVE to now.
(Note: This last book rubs many people the wrong way. If a specific situation irks you, ask what principle he was applying, and if it could be applied to a situation that doesn't annoy you)
Authority:
http://www.amazon.com/Authority-Become-Following-Financial-I... http://nathanbarry.com/authority/
Start Small: http://www.amazon.com/Start-Small-Stay-Developers-Launching/...
SEO: http://moz.com/beginners-guide-to-seo
4HWW: http://www.amazon.com/The-4-Hour-Workweek-Anywhere-Expanded/...
I read it in 2013, and it's probably earned me at least $100,000. That's being veeeery conservative.
Not everyone will have that experience, of course. I had an existing book series, and Authority gave me an idea for how to repurpose it into a larger business.
As for the package on his site: he probably wants to avoid support. You get a lot of it with a $20 price point, and as he wrote in the article, he's focussing on converkit. Whereas with the amazon listing, amazon handles all customer support.
(I learned that lesson with my own books. My amazon royalties are smaller than my overall business, but I'm still very glad to get them, because there's basically zero admin work required.)