If you are looking for a cheap CB and or CDM for strength in depth you could do a lot worse than Callum Chambers. still only 28 and Emery is not a fan, he sent him out on loan at Arsenal and doesn't play him at Villa. But when he has played for Villa he has done well and is a clever player. He was out on loan at Fulham (from Arsenal) and he won their Player of the Season playing as CDM. He is not world class but he has lots of PL experience, got a few caps for England, and is a very competent backup or starter for a PL side. Villa signed him for free and he is out of favour so he would probably be ridiculously cheap for a PL CB that has experience.