You can sell your ebooks through Amazon's Kindle program or Apple's iTunes Connect, which gives you access to a large majority of the digital-book reading market and the barriers for entry are incredibly low. You don't need to invest lots of money to make this happen, but you do need to invest lots of time, not only in writing the ebooks, but in marketing them as well.
Well, actually you do. There are over 500,000,000 (yes, 500 MILLION) products that you can promote as an affiliate marketer online. This means you don’t have to carry any inventory for any of these products/services. You simply link to companies through your special affiliate links, and exchange and they give you a cut (%) of every sale that you make.
The audiobook industry is booming, yet only 5% of books ever get made into audio format. If you’ve got a background in acting, or if people have said you’ve got a voice made for the radio, you can make extra money recording audio versions of independent and popular books. Sites like ACX connect authors with audiobook performers. So, whether you’re an author looking for more ways to sell your book, or an actor/voice actor looking to make some extra income, you can sell your services online.
If you're interested in online marketing, setup email software and create a lead magnet that you can use in your sales funnel. Then, build up that list. It's often said that you can expect to earn about $1 per subscriber per month. If you have a list of 10,000 subscribers, that means you can earn roughly around $10,000 per month. You will need to deliver value and not pitch them on every email, but it is a very achievable goal in a short period.