This effectively gives you 7GB for $50 (and you get a Mobile Broadband stick thrown in there as well.)
Credit expires in 30 days unless you recharge.
Pretty good per-GB value - even if Vodafone's service around your area is iffy.
Find it in your local Woolworths catalogue, page 14.
DSE also have a few prepaid deals atm (these are the "older" devices though?):
Vodafone Pocket Wi-Fi Pre-Paid Mobile Broadband (3GB / 30 days) - $39.50 delivered
http://dicksmith.com.au/product/E6783/vodafone-pocket-wi-fi-…
Telstra 7.2 WiFi Pre-Paid Broadband (5GB / 90 days) - $79 instore
http://dicksmith.com.au/product/E6793/telstra-7-2-wifi-pre-p…