Bryce Harper will become an unrestricted free agent after the 2018 MLB season. He's making just south of $14 million in 2017 and will make $21.625 million in 2018.
He's almost certainly going to dwarf those numbers when he signs. An American League general manager told ESPN's Eddie Matz he expects as much. In fact, he went so far as to suggest that $400 million over the course of whatever contract he gets is a low estimate.
"Four hundred million is light," the GM said. "It's going to be more than that. If you could sign him to a 15-year contract, you do it. I would say something in the range of $35 million a year, maybe closer to the high 30s. It could approach $40 million a year."
This may sound absurd at first, but Harper is one of the best position players in baseball and other players are already making more than $30 million per season. Arizona Diamondbacks starter Zack Greinke will pull in as much as $35 million (including signing bonuses) a season over the duration of his contract. Miami Marlins slugger Giancarlo Stanton will make upwards of $32 million in a single season on his.
Either way, Harper is on his way to becoming the highest-paid player in the sport, at least until Mike Trout (who will make $34 million per season starting next year) becomes a free agent after 2020.