id be happy to sign him for £20m. he has a world of potential. if he doesn't develop in 2 years, you can sell him back to a club in germany for £10-15m at worst.
if he has a monster season in 2015/16, his value goes up again. if we're not going to shop in the very top bracket, we should be trying to sign players in that next bracket, and also players in the "could be awesome' bracket. those players still go for decent money.