まとめ買いが安い

http://www.aliexpress.com/store/product/20PCS-LOT-Free-shipping-HC-SR04-to-world-Ultrasonic-Wave-Detector-Ranging-Module-HC-SR04-HC/213957_1490045036.html

http://www.aliexpress.com/store/product/10pcs-lot-HC-SR04-Ultrasonic-Module-Wave-Sensor-Ranging-Detector-Distance-Module-for-Arduino-Free-Shipping/406986_760308633.html

http://www.aliexpress.com/store/product/Free-Shipping-10PCS-LOT-GY-271-HMC5883L-module/213957_1490071694.html

http://www.aliexpress.com/store/product/10Pcs-Lot-GY-271-Electronic-Compass-Compass-Module-HMC5883L-Triple-Axis-Module-Magnetic-Field-Sensor-Free/406986_915920245.html

http://www.aliexpress.com/store/product/5PCS-lot-IIC-I2C-1602-Serial-Blue-Backlight-LCD-Display-For-Arduino-2560-UNO-AVR-A004/406986_1406625616.html