We've become accustomed to prepaid 3G broadband dongles selling for increasingly discounted prices, and here's another sub-$20 deal. Optus subsidiary Boost Mobile is selling its dongle for $19 with 2GB of data included, and online store PCC has the same deal with a more generous 5GB of data.
The major concern with this deal is Boost's data structure: data is charged in 10MB increments, so you can chew through it pretty quickly (though Facebook and Twitter don't count against the total). It's also network-locked to Optus unless you purchase a $100 recharge. As a low-use Optus dongle, though, it's one of the cheapest deals we've seen (Virgin Mobile often has similar specials, but is charging $29 right now with a lower data inclusion).