Best free or cheap software / service for SEO monitoring?

I am working on a site that has just drop from 3rd place on goggle to 9th and I have no idea why.
Does anyone have any recommends for free or cheap software or service for monitoring your seo performance?

Try one of these -
SEO Book for a Keyword Research & On-Site Analysis, SEO Site Tools for On-Site Analysis & Suggestions, Open Site Explorer for Competitor Backlink Research, SEMrush for Paid Search & Keyword Ranking Analysis, Authority Labs for Monitoring SEO Campaign Results

Hey Black Hat Pivot, sorry to hear your rankings dropped. There are many areas to consider if your rankings drop, so yes, you should be running a full audit to determine all areas that can be fixed, or improved.
I can suggest a free (or cheap) suite that can help in your case-SEO PowerSuite. It has 4 tools inside:
-SEO SpyGlass- so you can audit your website backlinks and then disavow the bad backlinks , check anchor text distribution ( see if its not overly optimized)
-Website Auditor- scan through on-page issues and get tips on what to do
-Rank Tracker- for keyword research & rank monitoring
and Link Assistant- for link building & management (in case needed)
https://www.link-assistant.com/

Search Console and Analytics cover a lot for free, especially queries, landing pages, clicks, indexing, and sudden traffic changes. Add a lightweight rank tracker only for your most important terms. A drop from third to ninth can be normal fluctuation, so, I mean, compare several weeks and check competitors before assuming a penalty.

A drop from #3 to #9 doesn’t always mean a penalty. I had start with Google Search Console (free) to check clicks, impressions, CTR, and keyword changes. For affordable monitoring, Ahrefs Webmaster Tools is also useful. Also compare your page with the new top ranking competitors and check for recent content, technical, or algorithm changes.

Google Search Console is probably the best free tool to monitor SEO performance I’d also check backlinks, technical SEO issues, and recent Google updates to find the reason behind the drop For affordable rank tracking, SE Ranking is a good option too

For quick daily tracking I use https://apps.apple.com/us/app/serpbeacon-rank-tracker/id6768772132, a free iOS app. It pushes a notification whenever my keywords move up or down, so I catch drops like yours the same day instead of finding out a week later. Good to pair with Search Console for the deeper analysis.

I'd start with Google Search Console it's free and gives you a clear view of your rankings, indexing, and overall search performance. If you want a few more options, Bing Webmaster Tools, Ubersuggest (free plan), and Ahrefs Webmaster Tools are all worth checking out for tracking your site's SEO.