As an engineer, I am borderline obsessed with learning how stuff works. This curiosity inevitably leads to the question "can I make my own?" Unfortunately, for most things, the answer is no; not without specialized equipment and tools. This however does not preclude assembling from existing parts.
Recently I stumbled on such a market for watch parts. Giving into my curiosity, I poked around the internet and tried to find a cohesive set of watch components that fit together; movement, dial, hands, case, stem & crown. Then I stumbled on companies that sell assembled watches from such components, for cheaper than the components, economies of scale I guess.
So I bought one from China. Here it is.
The case design somewhat resembles a PP Aquanaut, that I like very much. The case is stainless with a combination of brushed and polished finishes. Miyota 21j movement, sapphire crystal, screw down crown. All for around $100.
I am not too sure about the sapphire crystal. However, it at least has a scratch resistant and hydrophobic coating.
The watch is very comfortable and feels solid.