There is a significant number of SEO tools to help conduct research and execute campaigns. Many are free, like Google Keyword Planner, Google Analytics, Google Search Console, and many others. However, many other tools required to conduct effective SEO campaigns together can cost thousands of dollars per month. Many tools like Ahrefs, SEMrush, and MOZ can help you with keyword research, on-page analyzation, content gap analysis, and backlink research. These tools usually have graduated cost, depending on the extent of use.