Though it sounds like these people are using CNC mills for the cases, that is definitely not cheap equipment.
Milling services are also available (and not super expensive in China) but the parts are very small, and there are a lot of them so it might not be a easy option.
The idea of printing the entire movement is certainly interesting though...
$500 SLAs gives you LCD SLA printing with medium resolution.
You will need at least $1300 for a Moai kit(with Laser Galvoes):
Or at least a $1500 DLP kit with a good resolution for creating small parts.
Fo really small parts you need the strength of steel or titanium. But you can made then in plastic, metalize the plastic and use something like EDM(electrodischarge) to make your parts.
I'll have to admit, I haven't seen what the state of the art is like. I did some googling of the printers you mentioned and the level of detail is pretty impressive (although most reviews were printing pretty figurines instead of engineering applications), so maybe 3D printing watch movement is not that far fetched after-all. That being said I'd still be quite impressed seeing a 3D printed watch movement. Even more so (and this is moving the goalposts) if the movement ran whole day on a single winding, demonstrating good meshing and low friction.