Easy YouTube Video Downloader offers a freeware version. It includes ads and slower speeds, but it is completely legal and virus-free.
Check bundle sites like Fanatical or Humble Bundle. They frequently sell "Ultimate Software bundles" where you can get Easy YouTube Video Downloader Pro plus 10 other tools for $15 total.
If you genuinely need the Pro features, here is the correct, safe, legal process:
Most Pro version software phones home to activation servers. The developer can remotely disable blacklisted keys, meaning your "free" activation will stop working within days or weeks.