TSL230R could be it - a lightintensity to frequency converter for $6 - Light Intensity to Frequency IC - SEN-08940 - SparkFun Electronics
datasheet: - http://www.sparkfun.com/datasheets/Sensors/TSL230R-LF-e3.pdf
Arduino Tutorial - Arduino and the Taos TSL230R Light Sensor: Getting Started | The Roaming Drone
Should get you started!
Succes, don't know if you can order easily in rural Tanzania ? However ordering might be the easy part 