theodp writes: Electronics almost universally become cheaper over time, but with essentially a monopoly on graphing calculator usage in classrooms, Texas Instruments still manages to command a premium for its TI-84 Plus. Texas Instruments released the TI-84 Plus graphing calculator in 2004. Ten years later, the base model still has 480 kilobytes of ROM and 24 kilobytes of RAM, its black-and-white screen remains 96×64 pixels, and the MSRP is still $150. "Free graphing calculator apps are available," notes Matt McFarland. "But smartphones can’t be used on standardized tests such as the SAT and ACT. Schools are understandably reluctant to let them be used in classrooms, where students may opt to tune out in class and instead text friends or play games. So for now, overpriced hardware and all, the TI-84 family of calculators remains on top and unlikely to go anywhere." So, to paraphrase Prof. Norm Matloff, is it stupid to buy expensive TI-8x milk when the R cow is free?