Depends on what software, and what kind of hosting are you using?

For shared hosting, you usually never have to pay for a control panel.. but when you have a dedicated server, you need your own license Im pretty sure, so cPanel and Plesk Cost money because of the license. If you're talking about a dedicated server, just go to the dedicated server website and see how much what panel will cost, some cost less than others, but usually cPanel is anywhere from 20-30$ A month more.