You are worrying prematurely about this. The latest figure I have is that Kaiser is paying 275k + 150k sign-on bonus, and having a hard time filling spots. If you want to build an insurance practice, might as well work for Kaiser.
On the other hand, I imagine cash only in Orange County or La Jolla would not be difficult to do if you have the right credentials (i.e. top program + right kinds of fellowships). This would allow you to hit a very different kind of ceiling (500k+ net, but likely a much higher year-to-year variability). I would focus on doing as well as you can med school and get into a top residency. The rest of the sweet gravy train will follow.