People are turning to audio and visuals when it comes to technical subjects. However, you should consider doing an ebook first and turning it into an audiobook through a resource like Audible's ACX platform. You can hire a producer either through a royalty share program, so you don't have to shell out upfront cash, or you can do a pay-per-hour hire as well.
I personally like this one for some spare cash. It does not take much to earn an extra $20 – $50 a week. Some claim that they are able to make a living by dedicating their time to different jobs at mTurk. You will have to go through a learning curve, but once you get comfortable, you will find plenty of good and interesting HITs (Human Intelligence Tasks) to work on.
The Field Agent app is available on Android and Apple devices. You only need to look for tasks within your area, do the research, submit the details of your findings and wait for your money. These tasks are simple and involve visiting stores and checking on issues such as display compliance, demos, and shelf availability. Each job may give you earnings between $3 to $12.