Wonderful to see such a well documented open source hardware project! It does show though how much more difficult these are than software projects. 3d design and printing, hardware sourcing issues, the need for careful component selection, very poor support for automation of the toolchain, etc etc. As a minor hardware tinkerer this is both impressive and daunting. Bravo!
It's all relative. It has gotten at least an order of magnitude less expensive over the last 10-15 years- 3D printing, low cost PCB manufacturers, availability and cost of automated machine tools like CO2 laser-cutters.
It has actually gotten to a point where often time is the most "expensive" component of hobby/open-source hardware projects- while the cost of CAD software has decreased (mostly due to competition and increased demand that allows to spread the development cost over larger customer base), the productivity of CAD-related tasks has not increased much, if at all.
