A good first step is to learn some form of CAD and buy a cheap 3D printer. With that, you can rapidly test mechanisms and ergonomics on a daily basis for pennies. With both products, I went through maybe 5-ish entirely 3d printed prototypes. This will save you a ton of money iterating parts that don't need to be made from the final materials. With some products, you can make something functional here, but in my case, plastic isn't stable enough to make gear pumps and grinding burrs with.

If you intend to use casting or injection molding, you need to start thinking about that now rather than later, and designing parts that fit those processes even if you aren't using them yet.

So now it's time to start working with final materials. The best way to save money doing this is to only make the most critical parts from final materials until everything is nailed down. PCBWay has reasonably cheap machining/metal 3d printing services but you can also reach out to CNC shops directly and build some relationships for later. For me, this meant making the burrs, pump, and group head from metal, and testing them inside an otherwise 3D printed machine. I could iterate on just those parts and not worry if they required downstream changes because I could just print the secondary parts at home. I also cast my own silicone to save money.

Then once you're happy, you can go ahead and have everything made from final materials, (even if those materials are, say, CNCed instead of injection molded) and you have your MVP. Production engineering is a whole different beast, but that is for another time.

As a disclaimer, I wouldn't recommend starting with coffee machines, coffee grinders, or anything like them if you want to make a physical product. Hydraulics (especially at a small scale) and material processing are difficult, non-intuitive, and will be impossible if you are learning the other core skills at the same time.