CWP has no uninstaller, since you are installing it on the clean "CentOS 6 minimal version" it completely modifies your system and installs tons of packages. The only way to remove CWP is to reinstall your server to the original state, like you had it before cwp installation.
How much the CWP costs?
CWP is completely free, but you can always make a donation to support this project and the further development. Donations: http://centos-webpanel.com/donations