From an internal cost justification angle....
Philip Crosby, the Quality Assurance guru, once said that "quality is free", because the internal (rework/redesign) and external (customer) costs were generally much higher than doing the job right int he first place.
Safety is a subset of quality (albeit a pretty important subset) and I would hypothesise that Crosb's rule of thumb is valid in this respect also.
Also, I'd argue that in the calculations in the previous thread, the impact of accidents on brand value has not been taken into account, a la Valujet.
It's one thing to despatch aircraft without catering (which will damage BAs brand), quite another to end up with pictures of a smoking wreck on global TV. In the latter respect, AF398 was a lucky escape (for the souls on board too.)