SEO tools are pretty essentials for your research purpose, make your life easier when come into competitor analysis and backlink building.
However, free tools and basic usage like ubersuggest, google search console, google analytics, google keyword planner and etc helps by giving you more insights about keywords, your audience behaviour and more for you to improve your website based on those data.
Personally, for starter, you can try using the free tools until you had mastered most of the SEO techniques and required reports for your website performance (maybe client need it by the time) then suggest to go for paid tools.
The cheapest - Mangools
The best so far (I been using, slight more expensive & more features) - Ahrefs
My basic guide of SEO - (SEO) Search Engine Optimization Guide 2020