During option choice, prices are calculated only in EUR, but once you choose the options and press the "Upgrade options" button, you have an order displayed, with a drop-down on the right just below the total to choose your currency below the total.
I just checked here, and it works fine here tested with Firefox and with Safari). If you still have issue, please tell me which browser and version, as this is a new feature of CBSubs 1.3.0 RC, and we want to make sure it works in all supported browsers.