Cheapest I've seen this (ignoring shipping).
A quick look on their website puts shipping between $9.95 (SYD, MEL, BNE, ACT) and $12.95 (HBA, DRW).
For those that don't know, this device when plugged into a screen, will allow you to send a signal from your laptop (or other compatible devices) to the screen. So you could use your laptop to send a movie to your TV, play a game or share photos with friends etc. Your device will need to support the WiDi technology though.
I've not purchased one yet as I'm still considering the significantly smaller Microsoft Wireless Display Adaptor which would be more useful for travel and presentations.
EDIT: looking at the specs, it only does 1080p and 5.1 surround sound.
I would buy a 1st chrome cast by adding few extra bucks which will cast my Android phone or chrome browser from desktop.