If you are searching an ultrasonic ranging module, the HC-SR04 is good choice: Its stable performance and high ranging accuracy make it a popular module in electronic market. It's cheaper than an IR range finder with similar range accurancy and distance.
It is a good plastic box for Raspberry Pi, which can protect it with one of these snazzy plastic enclosures?. These cases protect the Raspberry Pi from things like rogue wires that might short it out while still allowing full access to the board! Simply snap the RPi into the bottom half of the enclosure, then snap the two sides together. The e