I graduated from high school in 1977. The very first time I saw a calculator was in "A" school in the Navy, later on that year. I bought one at the Navy Exchange, can't remember the price. It was a Casio calculator, I can't remember the model number. We used to get drunk and use it to play music on our stereo in the barracks room. Tune an FM radio to an unused frequency, lay the calculator on top, and just press the buttons. The radio would pick up the frequencies, demodulate them, and play them back.
It was fun, but the music was somewhat limited ;)