For an industrial setting funds are not unlimited but the value of the machine to the process is known or predicted and if the benefit is greater than the cost, the funds are sought.
Relationships with suppliers are built up over time. A lot of these relationships are old, passed from one team member to the next. Typically one maintains a relationship with multiple suppliers of similar capabilities to reduce the risk if something happens to any one supplier. So you intentionally buy product that you know will be more expensive or lower quality to keep the relationship established.
You will have to work to find suppliers and build those relationships.
You are also working with prototype quantities which adds another challenge into the mix. Some suppliers (whether it's machinists or components vendors) don't like to waste time with small fish. It's not worth the effort and there is a higher risk to them of not getting paid. That's kind of the way it is.
I've worked in robotics prototyping for a long time, for both institutions and small but well known companies. Working with prototyping quantities (2-20) has always been a tough sell. You start to get a feel for whether the supplier will work with you pretty quickly.
That said, if you do your leg work you can find everything you need. For instance, I needed a custom bearing made and the big guys laughed at me because I needed less than 100,000. But I called around and got lucky, finding the small shop that did prototypes for the SKF research team. On the other hand, I needed A custom gear+shaft and one of the big companies that normally does stuff for helicopters slotted the design right in with no problem. You never know. You just gotta pick up the phone. A lot.
Regarding costs it's unclear whether this is a personal project or a startup one. If its a startup, try pitching your design to investors or directly to your market. Even if you want to self fund this serves as a good test, if neither are breaking out their wallets, this should be a big warning to you that the world is not ready for your idea. I've had several friends, with PhD's in robotics from good universities, throw a way a lot of money on failed startups that did not meet this test.
If it's a personal project you may have to resort to dumpster diving and other similar techniques. Bosch may want 5K for their light weight high performance valves, but the Ferrari racing team (or whomever is near you) is probably throwing out some because they have 10 hours of use and the driver is complaining.
The phone is your friend for the industrial components and services world. You'll get a faster response than email. It may help for you to throw up a 1-3 page website for your company (make one up if you don't have one, a sole proprietorship) that the sales guy can hit.
Finally, if you don't have a lot of experience with hydraulics, spend some time researching degloving to get proper motivation for your safety protocol. A small exo with no barrier between me and the hydraulic lines is not something I would get into.