You are paying for hosting. Wordpress the software, is free and open source. Some plugins and themes may have a cost associated as well. There are lots of affordable WordPress hosting options out there. I pay about $50 a year.
Discussion
Looks like I'd be paying to access plugins, too, lol.
That seems crazy. I use hostinger, just for small personal stuff, and it works fine. I think it is cheap because there isn't a lot of hand holding by support, but it works for me.
Any webhost can host your site for a few bucks checkout HostGator or bluehost