I strongly suspect a working setup could be made for <$50 in electronics parts. The LabJack ADC, Phidgets DAC and Photodiode make up nearly $450 of the total c

I strongly suspect a working setup could be made for <$50 in electronics parts. The LabJack ADC, Phidgets DAC and Photodiode make up nearly $450 of the total cost. An Arduino, breadboard and a few components could probably do the same for a whole lot cheaper. The concept of "low cost" here is relative to a dedicated lab watt balance machine, which is probably thousands of dollars.