cPanel:
If you want a Windows server, you can't use cPanel.
The cost of cPanel varies depending on whether or not you install it on a dedicated server or a VPS. The latter costs around half as much as the former with a yearly license of $200 as opposed to $425 for the dedicated version.
Plesk:
Unlike cPanel, Plesk offers support for a much wider variety of operating systems including variations within Linux itself. In addition to the three Linux OSs supported by cPanel, Plesk can also run on Ubuntu, Debian, and openSUSE.
Like its primary competitor, Plesk also has two separate schemes for VPS and dedicated installations. Unlike cPanel however, Plesk has a much wider range of licenses depending on the number of domains you wish to host, whether or not you want to include packs like WordPress and the developer toolkit, and whether you want to bundle it with CloudLinux.
DirectAdmin:
Like cPanel, DirectAdmin also only runs on Linux systems, specifically RedHat, CentOS, FreeBSD, and Debian.
As far as pricing options go, DirectAdmin certainly has the simplest setup with no distinction between VPS and dedicated environments. For a recurring payment, you can either choose a monthly, quarterly, or yearly license.