Economies of scale. It looks like they are targeting ~150 of them to ship ($135,000/$900 = 135). If I assume their non-recurring engineering costs is %50 of the price, that means the budget for designing/tooling/etc. is $67,500, which is actually much, much lower than I actually expected.

A Macbook on the other hand is targeting millions of devices. If we assume, let's say, a Macbooks budget for the same thing was $500M, selling only 10M puts the individual NRE cost to be $50.