Hello, yes there is a fee associated with the Plesk control panel.

The Plesk licenses have a $10 install fee.

10 domains - $10 / month
30 domains - $25 / month
100 domains - $35 / month
Unlimited domains - $45 / month
Language Pack - $6 / month
Power Pack - $15 / month

It would be cheaper for you in the long run to go with the Plesk deal rather than purchasing a license on your own for the control panel - but yes, you could get it control panel-less which would mean you'd have no easy way (via the browser) to access your account and settings.  For more VPS related questions, I would suggest dropping in an e-mail to vps@lunarpages.com.  Thanks!