Feedvisor: Very expensive algorithmic repricer that optimizes your margin by trying to win the Buy Box most of the time and takes into account other factors that affect who wins the Buy Box aside from price. Unlike any other repricer, it will raise your price (again, within limits) if you can still win the Buy Box despite the higher price. It also has a bunch of other great reporting and tools.
Believe it or not, you might already have most of an ebook written already. If you are already making money with a blog, those blog posts could be turned into an ebook with some editing. Simply collect relevant blog posts into an order that makes sense, make any needed edits so that references that aren’t relevant are taken out, and add an introduction and conclusion, and you’re done. Any blog posts you use should cover the same or related topics and work well together.