There's a list
here. Just like all day and/or state schools, they're all completely different so it's best to choose a few favourites and go to their open days before you make any concrete decisions. (Beware that quite a few boarding schools are becoming IB only in 6th form so won't be of any use to you.
As for price, £24k is about average I think (I went to King Edward's Witley but left before 6th form, so my fees were slightly lower). For a top school you'll probably end up paying around £30-£35k, but there are other costs involved like uniforms, deposits, house funds, trips, educational supplies etc.