The Pro Version costs 8.99 US$ or 8.99 €.
Over the time several extension packs or special feature will be added which requires a additional InApp purchase. Currently the first extension are offline hillshades you can apply to all maps.
The Pro Version has a lot of more functions, not only offline maps like some users thought. → Summary of the extended features
Buying the Pro Version has NO effect on the restrictions for Basic Members of geocaching.com. These restrictions applied to all apps using the Geocaching.com LIVE API. → More informations about restrictions for Basic Members