When you say a grad student’s income, you mean the income you get from having a master’s or higher degree, right? You don’t mean your wife stays home and you go to school on an assistantship, do you?
At this point I am a PhD student. In the past I’ve made much more and in the future I hope to do so as well. But we’ve “taken a vow of poverty” for 4 years to get this accomplished.