"For example, a mechanical engineer is someone that designs mechanical systems. In order to do that, they will need specialized and very expensive equipment, and the end result will be produced with machines costing hundreds of thousands or even millions of dollars."

Not really. The difficulty to manufacture something isn't tied to the ability to engineer it. In fact, good engineers try to make the item easier/cheaper to manufacture. Take the AK-47 vs the M-16 - one used more exotic (for the time) materials with a more expensive and involved production process. The other was made with looser tolerances out of cheap stamped steel and wood that could be cranked out quickly. Yet they were both (eventually) of similar effectiveness.

These days, we have CAD and 3D printing available to craftsmen. If you want to build it out of metal and make it reproducible, you can build and print the parts to create molds to cast them from. Same thing for people how have a lathe and/or milling machine. In some cases you can get them used for a few hundred dollars. Record your dimensions and process and you can crank out copies of items with great results - no engineering training needed.

Was the AK-47 first built and designed with stuff a normal mechanic would have had access to at the time? And to test it? And produce it at scale? That's engineering work.