> You know why open source hardware is expensive for lower quality? Because Apple pays the premium on the premium quality stuff. But I'm that process they also drive up the prices.
Hardware is hard. Some Atmel or whatever low brain microcontroller can be had on a board with hand-painted selfmade-etched circuits or shoddy breadboard stuff, at the frequencies these things operate signal integrity doesn't really matter.
But anything with a brain powerful enough to run Linux? Then you're delving into differential signalling at extremely high frequencies - which means you have to precisely account for trace widths, trace thickness and trace length matching simply to ensure that the signal from your CPU arrives at your RAM chip intact. You'll ned an awful lot of awfully precise voltage levels other than 3v3/5v, with equally precise requirements on timing in getting them up. You also won't be able to get away with a two layer board, you'll need three or more layers and a lot of vias - and now, you can't manufacture your own prototypes any more but need to order at a PCB shop which means you either pay through your nose for speedy turnaround and low volume or wait for weeks for pool orders.
And once you have the PCB you'll need to populate and solder it - where you will run into such nasty things as minimum order quantities and the need for a pick-and-place machine if you don't want to go nuts. And if that's not enough, have fun with NDAs and no support for hobbyists by big SoC vendors due to small volumes (I have extensively written about that topic here: https://news.ycombinator.com/item?id=25208056).
The best solution if you needs smarts is to look into either adopting a Raspberry Pi 4 Compute Module if you can get away with its performance, or look into COMexpress if you need serious, up to Intel Xeon scale levels performance - but be warned, designing for that ain't exactly easy either.
