Which the customers did not have to pay for.....
They would if they'd ordered it specially and only bought 12 A Classes. If they only made 12, each one would have cost $125m. After the elk problem, each one would have ended up costing the customer nearly $150m.
As it happens they sold over a million copies of the original A Class, hence the cost growth would have amounted to less than $250 a unit. This cost may have been passed on, who knows?
The business/finance models between selling 12 and 1,000,000 of a given product are clearly quite different, but the principle point is that late emerging problems in complex engineering programmes are expensive to fix, and can be a significant proportion of the original development estimates. Its not just "evil complacent etc. defence contractors" who regularly face such challenges.