Zero, Nada, $0, you get the idea. The software can be downloaded for FREE. It has features that can be used with Wirecast even without our hardware interfaces. Take a look at the long list of features that are in the software.
However, there is a premium version that adds some really nice features and removes the ads. Take look at Wirecast Remote Pro on the main product page. These include the ability to map midi inputs to shots, an onscreen virtual switcher and much more.