[crgwbr]

Same here. Even the small motors were expensive at the time. One winter my dad and I figured out how to make our own—rolled the casing out of packing tape, poured the end plug from (I think) Durham‘s rock-hard water putty, then filled with fuel made from a mixture of black powder, sugar, and salt peter. The next summer, getting to use up all the engines we’d stockpiled, was glorious.

[tlavoie]

I had (maybe still have somewhere?) a book I'd ordered online as a youth, on how to do exactly that. They were somewhat fiddly, in the sense of being slightly lower-impulse, with clay nozzles and a hollow fuel grain. Never quite got around to making any. I should look for that book though. In any case, it's likely harder than it used to be to get saltpeter, which they just carried in the pharmacy.