$10,000/month! Enough of the guru stuff, let's talk reality...what's it really look like if your goal is $500/month?

YES, I realize that most self-published books never sell more than a few copies. I'm just curious to hear some stories from people who have had a taste of success.

Looking for feedback from people who are at this level or above. I'm not looking for fairy tales, hopes and dreams or guru talk. This is side income for me. My dream was to write a book. Even if I sold 0 copies, I just wanted to get this idea out of my mind and sitting on my shelf as a published book. Then, as I worked through the process I realized I really enjoy this and want to write more books. I'm not looking to "get rich quick", quit my day job or retire early. Just make a little extra money. Maybe a car payment? lol I can dream, right!?!

For those that have reached this level (about $500/month USD), what does this look like FOR YOU?

How many books? Constant marketing? Do they develop some momentum and eventually require less marketing? How many years ago did you publish your first book?