You need to buy a membership to Sam's Club to be able to shop in their stores or pay the advertised online prices. I think you may be able to buy online without a membership, but they will charge a premium.
SOCOM bundle is the best deal, the mic brand new is selling usually at $49.99, so you might aswell pay the extra $10 and get SOCOM (great game now that it has been patched) for $60.00 and go wild.
With what I've seen at Circuit city, with it being 30% off on controllers, cards, and of course the headset, than it'll come out to $35 I believe. So other than getting the socom bundle I believe that's the best bet to get the official headset.