The largest Counter-Strike prizepool so far was ~$500,000. And, while Quake, Starcraft, WC3, and original Counter-Strike certainly had tournaments and a devoted following, the scene has exploded to a much larger audience and larger prizepools in the last few years, primarily on the back of streaming services like Twich and games such as Dota 2 and League of Legends.

http://www.esportsearnings.com/tournaments