Please. Who, in tech, is making $300 to $600 an hour "base salary"? Pretty much nobody other than a handful of VPs and CEOs. None of which are likely able to to do a real technical interview anyway.
That said, the same is true across all these pricing tiers. I wouldn't consult on a Junior level interview for $60/hr, much less $30. I can earn twice that as a W-2 contractor doing boring, unchallenging enterprise architecture and software.