> They built their platform from scratch.
Yes, but SpaceX makes rather different ship from scratch. Crew Dragon should be nicer to ride than Soyuz - more space, better aerodynamics. But better qualities don't mean less price.
> The Russians are using 1960s tech still.
Yes, but that makes some tech more flight-proven and amortized over time. Like rockets - Soyuz and Proton are old, but quite inexpensive (albeit with reliability issues lately). At the same time, lots of internals of Soyuz were changed.
> It also helps SpaceX that Russia is always threatening to embargo exports of their rocket motors.
Fully agree here. But that's not quite economical issue.