If a player is taken on a waiver claim, as is the case here, the new team picks up the contract. It's only if the player passes through waivers, and the current team then chooses to release him, that a new team can pick up a bargain. / edit - of course, for anyone on a MLB-minimum contract, such as Mejia has, the business of what get pro-rated is moot. If eventually he were simply cut, and then someone else picked him up, everything is based on the minimum and what remains of the season.