SEO isn't hard. It's time consuming. I have several websites (one is my main business and the others are adsense sites). All my sites rank high. My main site is number one for organic searches...I'd say roughly thirty plus keywords. I don't pay a dime. Though I paid a lot in sweat. The rest of the keywords and there are hundreds rank in the top thirty.
I clear six figures with zero advertising dollars. None. Zero. Zip. But again, it is time consuming. You have to be patient. In the end, however, it is all worth it.