Looking at the Hosting Server Bulletins, it appears that CentOS servers do have node.js. (It's mentioned as part of the latest upgrade.) You could check if your specific server mentions that it's CentOS-based. According to various entries on lunarpages.com, it seems to be available under Plesk and possibly other OSs. I don't see anything about it being an extra-charge feature, but I can't rule it out.
If you have a small amount of sample code, you could try it on your server. Or, you can open a support ticket, asking about node.js on your specific server. It's possible that you might have to switch servers or plans to get node.js support. I don't use node.js myself, so I can't tell you if it's widely available (like PHP) or is restricted to certain servers.