Second, the mold itself is made of a very hard steel, though there are cheaper "soft tooling" materials for making lower quantities before the tool is worn out. The special steel may require special machining processes. The tool also has a variety of moving parts such as ejector pins and other mechanisms if the part is not shaped to be ejected cleanly.
If the mold comes from low-cost supplier, there's the added cost of reworking it in order to iron out minor problems. I spoke to one tool-and-die machinist who told me most of his income came from repairing cheap molds.
If you save on the mold, you often pay more for the pieces due to scrappage, difficulties setting up the molding machine, or the short lifespan of the mold.
Right now I work in a business that makes expensive high-tech equipment, so we can afford to eat the cost of making expensive parts from expensive molds.
For prototype quantities, we tend to prefer things like folded sheet metal, CNC, and even small aluminum castings with secondary machining processes. In that milieu, the cost of 3d printing is actually quite competitive. I just got some pieces costing about 1000 bucks each, but they were delivered to my doorstep a few days after being designed.
Also: Something I've learned is that everything I know might be wrong tomorrow. Every manufacturing process is being steadily improved, and a process that you wrote off as being too expensive might have suddenly become cheap for reasons you're not aware of. Always ask.
I do a lot of 3d printing but have run in to the limits quite a few times where I want something bigger than my print volume allows, or I want something water proof, or food safe, or I want something transparent (which can also be used outside), or I want it smoother...
resin printing or finding someone with a big printer... these things help sometimes.
Another trick I have yet to succeed at is using some existing plastic part, or transparent plastic from a soda bottle... Repurposing for these edge cases.
I get that the parts are 3D printed, but are they being printed on-demand or something? I wonder if the 3D printing files have been open sourced - would be interesting to hear from a 3D printing enthusiast here about the costs (it's HN, there's bound to be many!).
There's a dozen things to print in the zip. I sliced 3-4 of them, and none seemed particularly heavy. Something like $0.50 of filament each for what I pay for PLA, which would put the whole thing at ~$6 of material. Perhaps the cost is being driven by some sort of print-on-demand costs?
FWIW, you could also buy an Ender 3 for ~$200, and $140 buys a lot of filament, so you could get into the 3D printing hobby for less than the quoted cost.
I bet you could CNC some injection molds the cost of 2-3 of these chassis. If someone could do that and sell the housing for ~$30 each, this would be an impressive piece of kit.