The highest I've ever seen ce costs go is 10k.
Though, even if the prices keep going up and up, there are players able to pay for the ce, I suppose, if they ARE getting that high. I can't imagine it going up to something astronomically terrible, but I do hope that ce stays at 7k-8k ish now, since it is manageable and you'd still have a little off the top after doing a Vana run or two.