Cheapest base...
Whoops, just forgot. When Mixed fleet comes on line, they probably will be the cheapest base, followed by LGW with LHR 'heritage' crews still showing as the most expensive. You'd have to have a sizeable Mixed Fleet presence in LHR to bring the average LHR cabin crew cost down to a level comparable with LGW.
LGW have had a rough ride for the past few years and have been on the verge of closure several times. It is a credit to the whole LGW operation that they have been able to get to grips with costs, punctuality and customer satisfaction and generally rise to the challenge.