Just go for regens... Really... No point you buy these players... If you are looking for a good CB who is not a regen and you don't mind the age, look at this Brazilian called Dede. He is beast if you bought him at the start but I am not sure how he looks when 2017/2018. Since due to the age, he is most probably much much cheaper already... Would recommend that even if you buy him, only spend a maximum of 10m due to his age sorry for long reply...
I don't know what Sakho is like in that season,but in the second season, he is seriously good,only cost £10.5million! He might be a useful experienced cb in your season! His rating was at 4 stars,potential of 4 and a half....
At this point in time regens, look at some of the biggest national teams and look at their u20s and see if you find anything you fancy
my cb partnership in mid 2016 consists of 31 year old agger and a german 18 year old called Hartmann