That poor man has had his life completely wrecked for no reason. Given the appallingly low prosecution rate for rape, it is astonishing that such a catastrophic police error could be made over one case they actually decided to bring to trial.
You ask how you put a price on justice - or the lack of it. I have no idea, money is no compensation for a destroyed life, but he will need a considerable amount to make up for lack of employment, housing, family costs, pension contributions etc.
Needless to say if this had happened in the States, his compensation would be very many millions, but then that's why US lawyers are so expensive. In this country we seek to take back accommodation costs for the time spent in prison. If this case has highlighted that injustice, then at least a tiny bit of good will come out of it.
Perhaps he can write a book with film rights, that might help with his pension!