The barriers to politics are manifold, intern pay probably lower on the list of reasons why there is little to none economic diversity in the ruling class. I mean most state and local offices pay so poorly that it excludes nearly any one who isn't wealthy or willing to live on crumbs. Any middle class person raising a family, even with a partner having a decent job, would rarely take such risks. One reason why poverty continues to exist is that the lacking education, lacking work skills, poor habits/attitudes are passed on through the generations. This is not a judgment, but an unfortunate fair generalization (one I don't blame the poor for). So a kid growing up in a poor household, probably hasn't heard about said-internship, much less has the requisite education, references, and grant/scholarship-writing-know-how. And when an exceptionally lucky (or plucky) poor kid breaks through, his kids don't suffer the same consequences he did, though his kid too may not be able to afford the education/experience to take on such a free internship. My sense is that people from poor households get knocked off the path for Senate internship long before they reach the question of whether they can afford to take the job.