A little over 50 dollars for an original 60gb with a headset, ethernet cable, and a 3 month Live card.
These should be sealed clamshell blister packs direct from Microsoft.
There's also an offer through Totalconsole.
Make sure you buy it from a seller that is listed as "Fulfilled by Amazon."
That way, if they are selling unofficial Microsoft HDs and trying to pass them off as the general article, you can have it sent back for free, and get your money back.