Who needs antivirus? As long as you're not stupid, don't use IE, don't go on random suspicious websites, and don't download random stuff, you're almost always fine. I used to run an AV, but they're just a waste of resources to me. Just get an active AV if you have to, a scan-only one like Malwarebytes. Wouldn't recommend not running one unless you're absolutely sure that you won't get a virus though.
But if you do want an AV anyway, just search "free antivirus program". Also, try
this. Avast is currently the top rated one there.