There are many keyword research tools available to you and most require a subscription where you pay per month for access to the tool.
I reviewed what may be the only exception to this rule.
Market Samurai is a software program that runs on your PC or Mac and (I believe) requires no server side infrastructure on behalf of the company (which is why they can sell it as they do).
The list price is $149. I obtained it on a trial license and on the last day of my trial license I received an email telling me I could buy it today only for $97. I did.
I've subsequently heard everyone who does not buy during their trial period gets the $97 offer, so you decide you do like it, wait for this email to save a few dollars.
My impression of the tool:
The one time fee with no monthly fees for anything makes it financial attractive, but.....
It's a very sophisticated tool which requires understanding and knowledge to use effectively. Market Samurai provides an extensive and useful collection of training videos which I had to watch twice.
So the "cost" of Market Samurai is not so much measured in dollars, but in your time and effort.
You must first learn to use the tool effectively, then you must put in the time to use the tool.
I give it 4 stars out of 5, but when I first started using it I would have given it 1 start if I had not persevered to learn it.
In summary, if you're willing to put in the time to learn it and use it effectively, it's a great tool for you. If not, it will drive you crazy and you're better off finding an easier to use tool.