You can download free trials, but they only last a month.
I know Norton stuff goes on sale in stores (Staples here usually), but I don't know about where you are. It can be up to 50% off and sometimes more if the product is an older version (like the previous year with a new version coming out).
If you are only using it for one computer, I think there are some that are only good for one and are a bit cheaper. There are also some for 3 computers (or even tablets and such) if you need that.
Free programs can be iffy. Some will scan your computer, but if there is anything you still have to pay to fix it. They might not update as much, so might not protect as well as paid protection.