You can see if you read the docs for that sonar-cxx plugin that it’s just an amalgam of other free and open-source C analysis tools. If cost is your only priority, give it a shot. It’s probably better than nothing.
If superior code quality analysis is worth at least $150 a year to you, consider requesting an evaluation of our Developer Edition, which is free for 14 days, and compare them both for yourself. The best way to know what you’re getting is to see the analysis results for yourself against your own code.