AFAIKtherearetwo ways in which you can use paypalpayments in DNN.

1. As a host you can charge people who use your dnn installation to setup addititional portals

2. As a premium for a particular security role - So to do this in your case you would:

• Setup a security role called 'Calendar Access'
• Under in the settings for the role enter a service fee and how often the fee should be charged to members
• Apply the 'Calendar Access' role to the module on the particular page, so it is only visable to users who are signed up to your site (free) AND subscribed to the particular role (for a fee)