They're probably more well off than the average college student, but if you have a regularly well paying job, buying one $50-100 figure a month isn't that unreasonable and wouldn't take too long to get a pretty decently sized collection going. And if you go conventions you can find them cheaper, so there's also that.
I guess, but you also need a sizable house/apartment to go with it. You'll probably also not have roommates to help cover rent.
But yeah, if they're spending all their disposable income on it, then I guess I can see it happening without nuking your wallet.