> It probably costs a lot more than $250,000 to develop a laptop from scratch (...)
Novena[1] had a total budget of ~750k$. It was done from scratch, with some nonstandard (and somewhat expensive) components (e.g. an fpga; it had a software defined radio included too, though it was a mostly-off-the-shelf-one).
Novena's a pretty amazing project, but it's not nearly as polished as this purism laptop appears to be. It's (intentionally) a hacker friendly box with lots of space and less integration than a normal laptop. It even uses a RC hobbyist style battery. Novena is a labour of love driven by a particularly skilled person.
To design and mass produce a laptop as slim and well integrated as the Purism laptop is significantly more work. To do so having never produced a laptop before would cost even more so. $250,000 really is a small amount of money when you're trying to mass produce cutting edge consumer electronics.
Of course they may (almost certainly do) have other sources of investment.
It probably costs a lot more than $250,000 to develop a laptop from scratch, so I wouldn't blame them for taking a higher level systems approach and buying in a pre-existing motherboard design. However, doing that inevitably gives up control of the design (which puts into doubt their claims of being completely open). If that's the approach they've taken, they're not particularly open about it.