Actually, McAfee is free and so is Symantec AV, with a catch. The US DoD has free versions of both programs and all their latest versions (personal, exchange, etc). They are free for military, and the military is allowed to give them away to friends and family at no cost. They are available on the Navy InfoSec website but you must be on a government network to access the downloads. Many people in the military don't even know this is available to them, so if you know anyone you can mooch off their benefits.

Also, ClamAV is free and portable...