Search for blogs that cover similar topics. Use a search engine and the search bar on blog hosting sites to find blogs that cover your topic or related topic. Read a few blog posts from the most popular ones, that show up high on the search ranking, have the most comments, or display a readership of 20,000 or more. Get an idea for how much interest and competition there is.
Have in-depth knowledge in your niche? Package it up into an ebook and sell it on your blog. I'd generally advise against selling it (at least exclusively) on Amazon or Kobo, as you'll probably be able to charge much less. If you've already built up a solid audience, you can probably change anywhere from $5 for a very short one, all the way up to $39+.
Notice that I avoided putting a specific dollar figure on the amount you can make from blogging. It will come down to your work ethic, your skills as a writer, your ability to generate targeted traffic, and plain old good luck. It’s a bit like baseball: everyone played it as a kid, only a small fraction make it to college ball, an even smaller number become professional, but only the cream of the crop makes it to the majors.
To all the bloggers out there…STOP sucking up to the very small, elite and narcissistic group of self-proclaimed influencers out there. If you all stop treating them like they’re special, they will not longer by special and therefore some of us who aren’t in there secret society will be seen as knowing what we’re talking about too! This isn’t High School, grow up and read someone else’s blog already!