Looking for confirmation of the fee, I stumpled upon this brilliant description of the young prodigy on a RM blog:
To call him a Xabi clone is an over simplification. Do they both dictate play from deep? Yes they do. Illarra is a much more mobile player though. He doubles up as the third central defender when his defensive duties are called upon. He tackles a lot better than Xabi does. Most importantly he is a lot more mobile than Xabi. Yes he doesn’t have the range, or that ability to find no look passes across wings, but that’s what I mean when saying they are not clones. If you like numbers to describe your player, he is about 60% Sergio Busquets and 40% Alonso .