Best and most cost effective antivirus program for PCs?

Hahaha, if you really need one, I think forget about anti virus, get anti malware like malwarebyte is more useful nowadays.

Anti virus just let your window defender to do it.

*A virus is a malware, but malware is not always a virus ;)

Use to have bitdefender together with malwarebyte, anti malware always detect faster than antivirus, and even what the antivirus cant detect

If you're on Windows, Windows Defender is good enough. Have been using it since Windows 7 and haven't had any issues