Best value for money is Pichu Atienza from At. Madrid.
£275k minimum fee release clause at the start of the game, he can become a bit better than Fazio, and doesn't pick up cards all the time like Fazio. Can also play DM or MC reasonably well too.
If you have large sums of money then Sakho is probably the best you can get though.
For me personally its been Scott Cuthbert who has came through the youth system lol. Ive never spent a large sum of money on a defender really so i wouldnt know to be honesty.