The grade part of this is the easiest to explain. In news you had to expect, given the Los Angeles Dodgers' hot streak of high-level pursuits, the champs landed a pitcher who might be baseball's top prospect -- one ready to join a big league rotation now -- in Roki Sasaki. And they do so with the same financial commitment as if Sasaki were an internally developed player who recently reached the majors.
In a way, the financial aspect is even rosier than that (from the Dodgers' perspective), as typically with a prospect of this caliber, a team might feel pressure to sign him to an early extension. With Sasaki, there's no such pressure: Any talk of an extension now would be viewed as circumventing the transfer rules. It's almost too good to be true.
However, there are costs beyond Sasaki's extremely team-friendly salary over the next few years. The signing bonus was limited due to the size of the team's international bonus pool, but it's still real money. And there is opportunity cost involved, because now the Dodgers can't sign a larger pool of international prospects. For this international signing period, all the Dodgers' eggs are in the Roki basket.
Obviously, the trade-off is worth it for Los Angeles. Not only does Sasaki further strengthen the powerful Dodgers, but they sidestep the ignominy of seeing him pick their biggest rivals in the San Diego Padres. Perhaps no team needed Sasaki more than San Diego, but it's the Dodgers who come away with one of the most impactful additions of the offseason.