If it's any consolation, it took Bordeaux a while to get used to his height too. When he was 16 he was played as a RB because everybody thought he was too short to suceed as a CB. It took a bunch of injuries from the first team's starting CB's to give him a spot in this position, but as soon as he played there he became a no-brainer. Goes to show how a player's career can be decided on luck sometimes. I mean, he's also pretty good as a RB (and he still plays there sometimes for Sevilla), but he really shines as a CB.
And yeah, crazy expensive. Bought for 20 millions 18 months ago, he was one of Sevilla's most expensive signing and one of Bordeaux's most expensive sale too, after Malcom and Gourcuff. So it's pretty obvious he's not gonna go for cheap unfortunately. Apparently Man Utd would be willing to pay 60-70 millions to get him this summer. I'd rather see him stay in spain though but at this price, I guess only english teams will be able to afford him.