Windows 10 already comes with a decent free Antivirus onboard called Windows Defender. It has matured a lot during the past years and has become very good. Good enough to land in top lists of several Antivirus testing reports.
No additional installation of software required as it is a core component of Windows. You can set things up properly. And with the last versions it integrates Antimalware, Antiransomware and actually also implements the Windows firewall as "Windows Defender Firewall".
No need to spend money on anything. Common sense together with Windows Defender, security and bug fix updates are worth more than paid software. Imho.
I spoke to the devil in Miami, he said everything would be fine.