The price for something he can’t have is something he can’t give. He thinks it’s pretty fair, so he gives it a try.
After seven long years of absolute misery, there’s barely anything left of who he was anymore. His own parents can’t recognise him, nor do the servants (who, in a way, know more than his parents will ever know) or brothers. Or perhaps it would be truer to say that no one is willing to acknowledge him, because he has next to nothing left. He’d thrown everything away for that one thing he couldn’t have, and everyone scorns him for it.
There’s only one way to heaven, and losing himself isn’t it, because even that isn’t enough as payment.