Sandoval is not a $19M a year player. Not even close. But he is lucky with his timing. He's average on D, and an above average, but not elite hitter. Should be paid, maybe $13-14M a year. If the Giants hadn't low-balled him at even less than that and only 3 years, they could have signed him for that earlier in the year.
The issue for Boston and others is the position. 3B is now the weakest position in the league across the board. There aren't any great 3B, and few who are even good. It's pretty awful. My main complaint is that the position is so terrible, that someone like Cechini is probably not far from league average. Hanley Ramirez, if healthy and playing average D at 3B, might have been the best in the game. It's a disaster of a position.