They're also very new, so they're not as mature as old machines. Older machines are massive and poorly documented, though.

This is one of the more polished micro injection machines: https://www.micro-molder.com/

This one is more industrial but seems better for continuous runs: https://www.apsx.com/desktop-injection-molding-machine

There are also several Chinese vendors offering reasonably priced injection molding machines now, but unless you're well-versed in the art of dealing with these vendors and DIYing your own support, they're not a great place to start.

If you just want to experiment, you can build or buy a manual lever-operated machine for under $500: https://busterbeagle3d.square.site/product/buster-beagle-3d-... These won't be powering any production runs, but if you're only interested in prototyping then they can be surprisingly effective.