Well i know windows has an update that installs one. But im sure you want somthing better. I dont have any suggestions, pretty much they all supply the same features. Just some are more user friendly. So i would just look around and get what looks user friendly and is not more then 50$.
But make sure you understand it before you use it. Because all firewalls do is regulate what comes in the computer and what leaves the computer.
What im getting at is if your trying to do things online, Firewalls are notorious for making it difficult. So just make sure you read the manual alot when you start using the firewall.
Finished With TF.