Talking of bust the reason Austin was only £4 mill is because that's what he is, a broken player lucky to "pass" a medical. And QPR would never have sold him to a Championship rival even if he'd wanted to go.
I think the reason he was only £4 million was a combination of
(a) He is out of contract in June, and as he is 26, QPR would have not received a fee for him in the summer., and
(b) He was on £70k a week, and Hasselbank has been tasked with reducing the wage bill.