"To me, true music is the expression of emotion and feeling through sound and such."
Not that I like him (I'm more of a Nightwish fan), but Soulja Boy fits your definition. Direct quote from Wikipedia: "In September 2007, his single "Crank That (Soulja Boy)" reached number one on the Billboard Hot 100. The single was initially self-published on the Internet, and it became a number-one hit in the United States for seven non-consecutive weeks starting in September 2007. "
So he's been doing his stuff long before money got into play. And from the lyrics of songs like "Successful", I can say his work is personal to him and has emotion. Sadly, I lack the musical knowledge/terminology to really help come up with a better definition, but your original definition of "true music" is definitely vague.