Other than phil jones, he is the best british centre back two seasons in so that sucks a bit. Good luck is all i can say mate, i can only reccommend rafael toloi or mario fernandes. Gary cahill can occasionally leave for around your budget.
You can check if Spurs let go off Kaboul or Bassong, they mostly let one of the two go pretty cheap or even on loan with a buy out clause. E.g. I got Bassong for 1.2m loan fee and 3.5m clause for Everton and while a lot of people that start a game with Spurs consider them trash they are both quality CB's with great potential.
Toby Alderweireld is quality as well and can be bought for 4.8m.