Pricing for the development SDK's are listed in the Products Details section.  The 3 levels of BACnet functionality start at $6,995.

The BACnet SDK's offer more and more functionality and are "backwards compatible". This means that all Device functionality is also in the Controller SDK, and Device and Controller functionality is contained within the Router SDK. The Router version is a very complete BACstac that is used by many of the leading HVAC companies in the industry.

You can download a spreadsheet which gives details about the functionality contained in each SDK from the documents section of this website.

These prices include a hardware prototyping board and one year of email and phone support and software maintenence updates.