https://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
Arduinocoms
— EZB v4-Arduino I2C bridge for ARC: supports custom C# code and reads gamepad or Wii controller inputs for robot control
Try it →
https://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.