Enterimvalve makes $2 million a day in revenues off this game last I heard. if they put even a $5,000 prize pool up for a tourney it would be ground-shaking for us little people.
no way do they make 30x the peak daily player count in dollars daily off this game.
that said even a $10k online tourney would be big for the game and would be relatively easy (lans come with lots of costs/time/liability). not sure how much of a profit tf2 makes nowadays but they've made bank over 9 years.