..., the motors themselves tend to be rather expensive.
My goal was to develop a system that could be used by high school students. It would involve proven rocket designs that could be flown on school yards. That meant it needed to be small, fitting everything into a body tube with a diameter no more than 42mm. This would allow it to use “D” or “E” motors. It would need to be flexible. I wanted the design to be a starting point to allow them to conduct real science and it had to be inexpensive.