$20 million is a bit unbelievable IMO, but until I see some factual reporting and not mere guesswork from a journalist, I'm gonna go by what the more reputable sources say.
I got the quotes from an ESPN.com article. Dan Rafael basically got his information from other media outlets. He doesn't have any conncections within the wrestling industry. Wrestlemania generated something $53 million in revenues last year. How could they possibly afford to pay Mayweather $20 million?