The International Open Source Hydrogen On Demand Builders Network.
If you have the time and patience to learn, try the cast polyresin method. This system is what sculptors use to replicate their works, and there are resins available that are highly resistant to acids and alkalies and can operate at high temperatures beyond boiling.
You can make patterns of parts using hard wax, and then you can form silicone molds over them. These things can be learned on the internet. This is what I'm doing now.
I must tell you, though that the first cost is as high as machining work, but when you replicate the parts, they come out pretty cheap. There's also some learning time to consider - about 1 week or more.