The Commonwealth Bank wasn't letting too many details slip about the NFC-enabled case it'll sell to customers at yesterday's Kaching launch. A quick hands-on shows the manufacturer, as well as how it'll handle the issue of charging while in its case. The case in question is the iCarte 420 (or presumably the iCarte 110 for 3GS owners, although I didn't spot any of those yesterday). It's a two-part snap-on case in basic black that hooks into the Apple dock connector for power.
In order to be able to charge the phone, a microUSB port at the base allows for charging. As yet, the Commonwealth Bank hasn't revealed how much the iCarte cases will cost; while the Kaching service itself and the associated app will be free, it would be surprising for it to offer them up for nothing.
I was told yesterday that it would "most likely" cost "around the same price as a normal iPhone case". That gives a range of anywhere from $5 to $100, though.