DocketMonitor is free. However, you still get charged from the PACER system.

You get charged when the system checks for updates. So when you first add a case, it doesn't automatically update, it just adds it to your list. When you click "Update", it charges you the normal pacer rate for looking at the docket. If you set it to automatically check for updates, you'll get charged every time it goes and checks. If you don't have it do it automatically, then it will only charge you when you manually update it.

The file system saves charges if you ever view a file multiple times. For example, if you go view a document off the pacer system, it charges you for the document, and if you go back and view it again (say you lost the document or whatever), it will charge you again. DocketMonitor will actually save the file on the docketmonitor server, and the next time you go to view it, it will NOT hit pacer, so you only get charged once for it.