Not sure if I should post this as a bug or not, but I think the game should disable the Gem store if it's running in offline mode - the same way it currently disable the reward calendar.
Prices shown in offline mode doesn't factor in the conversion rate and are therefore incorrect.
Offline prices - probably USD
Online prices - converted AUD
Prices shown in offline mode doesn't factor in the conversion rate and are therefore incorrect.
Offline prices - probably USD
Online prices - converted AUD