BAE clearly under-bid on price when they won, and were, I believe, asked several times if they'd done their sums right. They said they had.
Well funny old thing, within a very brief time of contract signing they asked to re-negotiate....and were given a frosty response. Quite right.
Unfortunately that was in the days when the DPA mantra was 'Pass all risk to the contractor' - which was utter rot, though moving DPA's thinking away from it was impossible at that time. They had to have a hard knock to realise that Technical risk can be passed off but Operational risk, and perhaps also therefore cost risk, remains with the customer.
So, we are where we are! That's the true cost with this airframe. Bad decision? Would the P3 have been a better one? No way of knowing and not worth the discussion now. Pay up and be happy, or at least smile.