Norton Antivirus 2011 For FREE

Frys.com offers software specials every week. Typically they offer about 5 different free specials a week.

Norton Antivirus 2011 With Registry Mechanic is currently $0 after rebate here

You pay $40 upfront, and then must submit two rebates for $20. 

It even has free shipping, so your only cost would be the taxes.