We have a full CNC shop in house with the latest equipment. I took a quick look at the design. It really isn't optimized to reduce fabrication cost. The CNC work on this leg is substantial and very expensive. It simply isn't designed for low cost manufacturing. I am not being critical, just stating a fact in response to your question.

In CNC machining cost reduction can be obtained through the reduction of what's called "setups" (how many sides of a part you have to machine), judicious selection of feature types (some types of cuts require the machine to slow down a bunch, special tooling or both) and fixtures.

The last one, fixtures, are custom made tools to hold the raw material and in-progress machined parts for machining. They can make a significant difference in cost. Without them a machinist has to spend a lot of time manually managing what is known as "work-holding" (how you hold the material for machining).

Beyond that, it's a matter of volume. If you are only making one set at a time, without tooling and without optimization to reduce CNC machine cycle time and tooling requirements it is going to cost a lot. If, on the other hand, the design is optimized for the process, part counts are reduced, setups are reduced and you pay for palletization tooling (allows you to make more than one part at a time) cost can be reduced substantially.

In addition to this if you can reduce or modify the size and shape of the parts such that you can fit, say, ten of them within the working envelope of a machine rather than five, it can make a huge difference in cost. This, again, requires the design of a palletizing fixture.

Fixturing and workholding for production of a few parts at a time costs money. Think of it this way: Each part you have to make requires a fixture to be made for every setup. In other words, if you machine from the top, bottom, left and right of an aluminum block and want to design a fixture to hold ten of them at a time, you have to design one fixture for each setup or side you are machining. There are ways to reduce this by working closely with the designers and optimizing for work holding.

You can also integrate work-holding such that one pallet can hold the part in different setups. In other words, you hold four parts in setup 1, four in setup 2, four in setup 3 and four in setup 4. A pallet designed like this produces four finished parts per machining cycle. After each run you move the parts to the next setup location. So, the four parts that were being machined from the top are moved to the right one position and clamped onto an area of the fixture designed to hold them for bottom machining. The other parts are similarly moved one position for the next setup and the parts on the last setup slots come out of the machine for finishing (clean, debur, inspect, post-process).

If you do the math on this the scope of the manufacturing problem starts to be revealed. If you have ten parts to machine, and each part requires, on average, machining from two sides, you need to design twenty individual holding fixtures. Some can be integrated into a unified multi-setup fixture but the design work isn't any different, in fact, it can be more expensive. If the parts require machining from four sides you need 40 fixtures.

Once you are done with mechanical design of the fixtures and setups each one of them requires CNC programming and tool selection. This is a detailed process that requires time, expertise and testing, lots of all of them. In a design like that of this leg the design, fabrication, programming and testing of fixtures can easily cost much more than what the posted cost for machining one set of parts.

In short, cost reduction for something like this requires detailed and intense engagement with the manufacturing process, which would lead to design changes necessary in order to reduce manufacturing complexity, machine cycle time, fixture count and complexity, material waste, etc.

One way they could have reduced the cost to manufacture these for other people could have been to, for example, pay for manufacturing fixtures to make four to ten of these at a time. Customer #2 would then benefit from this and possibly cut their cost by a substantial amount (25% to 50%). At the limit the cost of machined parts become asymptotic with material cost + hours on the machine + aggregated costs-per-hour for the shop (people, wear and tear, power, etc.).

It's an interesting project. If the market is large enough it might make sense for someone to pay for the design and fabrication of the tooling to offer these parts at a lower price.

At a larger scale you'd have to design the parts for a casting + machining process, which will make them far less costly.

Metal 3D printing might be another option but that's not as cheap as one might think and has its own design requirements.