Nicolas Otamendi is your man! For 9,5m he is very consistent on my save. Only 22 at the start, 17 marking and 18 tackling, speed and can score via headers too. Phil Jones is great investment for future too
I don't really see why anybody needs to mess with the City squad. Kompany and Toure won me everything at club level. Lescott is top backup and Boyata becomes class also within a couple of seasons.
You only ever need to buy kids for the future at City.