I'd assume the coffee geeks have figured out how to make cheaper machines and put the designs on github.

They have, kind of. Check out Gaggiuino. Sadly not really open source (Gen3) but you can get a cheap $500 Gaggia Classic and add fine grained control with an Arduino and display: https://gaggiuino.github.io

Then there's the really open source Rancilio PID Clever coffee project:

https://github.com/rancilio-pid/clevercoffee

Different machine, similar approach, a bit more DIY since you can't buy a kit.