Algeraist
Australia
Asked
— Edited
http://www.dealextreme.com/p/hc-sr04-ultrasonic-sensor-distance-measuring-module-133696
DX is a good site but always takes a while to ship - I'd allow 3-4 weeks in Australia at that is...not sure about US times
Even cheaper on E-Bay.
I recently bought (6) for 2.50/ea.