He would be able to make twice as much in salary if he went to Europe but he'd probably lose more money in the long-run by not playing in the NBA.
I get the feeling that Lebron will be able to leverage the Chinese ties which a new minority owner of the Cavs has and find a way to tap into the fledgling basketball market in China. Yao Ming has opened up a gigantic market for the NBA and someone is going to make a lot of money off of it.