That's often not true; PCBs can be a significant cost on the bill of materials for a gadget.

Amortising the tooling / artwork costs into big volumes helps, but even then the PCB is usually one of the more expensive items on the parts list.

Yup, it was interesting reading some of the discussions about the design of the device. PCB cost was a major consideration. They aren't exposing some of the I/O pins on the SoC because it would require a more expensive PCB to do so.

Custom small-time boards get expensive quickly when you shoot for tighter tolerances, which are necessary for truly tight spacing. If Raspberry Pi expects to sell 10 million units, then even a fancy board will cost nothing, but I doubt they are planning on such numbers...

Board design is expensive for small units - but assembly costs for complex boards don't drop very much with large numbers.

Especially if Apple have every super high-end pick and place robot booked for the next n years!