One way to make money online is by selling electronic products also known as infoproducts. Assuming you already have an ebook (which can be a simple MS Word .doc file or even a PDF file), you can easily make it available for download to paid customers with the help of a free Paypal IPN script.
The one I tested is called Simple IPN, and it works quite well with digital download products.
You can store your downloadable ebook (or even MP3 audio file) in a non-public or non-accessible folder of your webserver. The IPN script then creates a temporary download link, which expires in X number of days.
The script allows paid customers to download your infoproduct even if your file is in a protected portion of your web site, and the download link automatically deactivates after a certain period of time.
It’s free, but you have the option of getting support from the creator, Iszuddin Ismail (@iszuddin on Twitter) for a nominal fee of just $10.
The download page that the script produces looks very simple, which means you can easily customize it (if you know a bit of HTML). Alternatively, you can easily find people you can outsource HTML design to, if you wish.