We're surely not so skint as to be seriously considering the tiny costs of an extra three crew members? Using the likely number of crews and assuming a generous average of 55 ish k the cost difference would be in the region of £2.5 million a year. Barely pennies in the grand scheme of things.
I'd suggest the capitation rates for Aircrew, especially if PAS or near the top of their payscales would be closer to £100 - 120k.
O.K., £5M per annum. Plus the cost of equiping the air-stairs with a Stannah stairlifts.