The salaries for bigs skyrocket, The giants are better but you cannot afford them.
but thats also a thing you have to consider, and i wouldn't be sure if it just the salary. i searched for one monster before my last cup game, and this lituanian 600k center, is pretty strong but i wouldn't be sure that he is stronger then Fagot who is probadly one of the best 5 PF on NT level even on Center position and get less then the half of his salary.
And if you want to train bigs, you also have to watch for B-Skills if you want to earn money and you didn't need 8 seasons of offseason farming for it. Even when you had to play them from time to time outside, but you do it most on position and there are always some weeks where you can do "crazy" stuff like that because your opponent plays crappy or is so good that you don't have to try.