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
MP3 Trigger
— Serial MP3 Trigger for EZ-B: plays MP3s from mini‑SD; configurable port/baud. Deprecated-replaced by EZB v4 streaming audio. 3rd‑party.
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.