Oh, I thought the question was what I do for marketing.
My book had risen to about 1200 in the Kindle store through word of mouth / 10 USD a day AMS ad, and then a prominent fantasy writer was given my book by a fan of his, read it, and he recommended my book, which led to a large sales boost. That wasn’t anything I did, though, so I wouldn’t call it ‘marketing’
That was about two years ago. In the meantime, to keep getting sales I run ads on the three cost-per-click platforms, like I said. Maximum spend right now is about 50 USD a day (10 USD Bookbub, 10 USD FB, 25 USD AMS - though AMS doesn’t usually spend its daily budget. The other two always do) . Works out to about 1k a month, I think.