They paid £12m for him, and that was with one year left on his contract. £4.5m is what Benfica received because they owned like 40% of the player, not unlike Rojo who is only owned 25% by Sporting.
You are right about Argentina having the best defence because of they way they played and not because they have the best defenders. Yet Rojo played very well for them and was one of their standout players for me. He is also still young and has some potential to develop, he is left footed which seems to be what we are looking for and he won't cost us anymore than £16m. I prefer him to Vermaelen and think that is a step up in all honesty, I also prefer him to Blind, as Blind sucks as a defender, just ask Ajax fans and is more at home in the position of a CDM.
Hummels is a pipe dream and so is Benatia, we are not getting those players this summer and anyway they aren't left footed which seems to be what LVG is after. I don't know anyone else but Rojo that ticks all the boxes for what we are searching.