Ian,
If the two prices were within 1%, two things are obvious:
1) The EH really, really lost on the merits, not just price!
2) If it were priced that low, I'd pass the hat to buy 1000 EH-101's just to cost Agusta-Westland $10 million for each I bought, and buy their factory machinery at the bankrupcy sale right afterward. It would be an interesting business tactic, wouldn't it!
Regarding commonality of savings, you can't save enough on commonality to make up for the 50% greater operating cost of an EH-101 vs. an S-92.
Regarding the cost of the equipment, the ASW gear they need is always very expensive, that is the nature of its technology. I read somewhere that the RN paid upwards of 60 million pounds each for their Merlins.