When it comes to SEO tools there are VERY few paid tools that I would recommend to anyone who doesn't have an agency or manage several clients.
Don't get me wrong, there are definitely some extremely useful tools out there. I've used all the fancy paid tools you can think of, and I pay upwards of $600/month for a select few, but there are free tools out there that can provide the everyday SEO with everything they need to be 100% effective.
From a price point, most every seo software is subscription based, meaning you pay monthly to use their services, and they are NOT cheap. So just use these 3 tools and save yourself a whooole bunch of money
1. Adwords
There are some ridiculously high-tech keyword research tools on the market, but they're just as ridiculously expensive. The coolest one IMO is SEcockpit, which is $100/month. I took advantage of their 30 day money back guarantee just so I could see what it was like, and props to them for a great tool, but Google gives you just about all you really need.
Get familiar with the keyword planner section in adwords and you'll be just fine. If you really want to get fancy with long-tails you can play with this free tool on top of using adwords
http://ubersuggest.org/
Keyword are simple enough..
2. MozBar
Now install the MozBar toolbar. This is my #1 favorite tool of all time. When it's on, it shows you the competitiveness of any keyword you type into google and a brief summary (DA, PA, # of links) for each website in the google results. This gives you a general idea of the competitiveness for each keyword, but the real magic happens when you go to a website.
On any page at the top you will have your basic DA, PA, mR, # of links, and social activity, but you can press the page analysis button and it gives you a dropdown that breaksdown the entire structure of the on-page SEO. It shows what words are being used in the title tag, meta desctiption, meta keywords, H1s and H2s, which keywords are bolded, and the alt text used on any images.
Then you can see a few details like page load time, the rel= cononical, if there are any 301s, a break down of the link metrics, and what type of markup is being used. Now that you've gathered everything onpage, click on the links info at the top, and it brings you to the Open Site Explorer. Which if you aren't familiar, the most basic funtion of OSE shows you each link that link backs to a site, the anchor text used, and the DA/PA of the site linking back.
Pro tip: Your competitors are your best seo source you have. COPY THEM! Check out each backlink they have to find easy opportunities to get links back to your own site.
3. WooRank Toolbar
Honestly MozBar/OSE is all you really need from tools for effective SEO, but there's one more bonus that everyone should have if they aren't confident in their on-site SEO.
Install the WooRank SEO & Website Analysis toolbar, go to your website (or a competitors) and press the icon. It will begin to perform an audit of your website that analyzes tons of different on site ranking factors, and then give you a score for each individual area, how important of a role it plays in your ability to rank, and a recommendation on what you can do to improve it.
It follows most of the standard SEO "best practices" so it's perfect for anyone without tons of hands on experience, but don't feel the need to treat this as a bible, just a general guideline.
That's all you need - right there on your toolbar ready to go the second you need them. And for those who want to venture out past these 3, here are 2 more free tools you can add to create an even more powerful toolbar.
(in order as pictured above)
1. SEOquake toolbar
2. MozBar
3. WooRank toolbar
4. Majestic Backlink Analyzer
If you're on a budget and do decide to pay for a tool, the industry consensus, as well as mine, is to go with scrapebox. It's a one time payment and it's yours forever. There is a bit of a learning curve, and it does require proxies, but with practice and the thousands of youtube tutorials available there's about a million things you can do with.
Now go get to ranking!