I used Keywords Everywhere a lot before when it was free. Now, the creators have made Keywords Everywhere paid. However, with the free version you can still perform decent keyword research.
With the free version, you won’t be able to see the search volume or other keyword specific data. However, you’ll find tons of suggested/related phrases of the search phase you typed into Google. To me, that’s good enough to do keyword research.
Once you have the budget, you can definitely invest into Keywords Everywhere for seeing all the search volume, competition data.