I'm actually an undergraduate student at CMU and through scholarships and Aid I'm paying about 22K per year (instead of 47k). So I would say they're pretty generous when it comes to aid.
With our graduate school, which one were you looking at? Tepper? Engineering? My Teaching Assistants are all graduate students and I know they get paid a good amount to teach the classes. They're all working on masters and Ph'ds with professors.
Also call the HUB at Carnegie. They gave me an extra 5k per year once I negotiated with them, they can be pretty generous.
Plus CMU is a great school, even if im biased