How much does the geo-referencing (Pro Plus) package cost?

Geo-referenced approach plates (terminal charts) and airport diagrams are included with the ForeFlight Pro Plus package subscription plan. This plan includes everything in the ForeFlight Basic Plus subscription and also includes Terrain Profile, Hazard Advisor, Cloud Documents, Flight Notifications, Logbook, Synthetic Vision, and Aeronautical Maps.  

Performance Plus also includes geo-referenced approach plates (terminal charts) and airport diagrams.

Details on both plans are available at https://www.foreflight.com/pricing