I thought USPS is the same as long as it is in the USA?
It is. But.... Although I am not certain of the exact weight of a 550 with accessories, I would have to assume that it is greater than 20 pounds. Priority mail on a package that big is still moderately expensive. Parcel post is slightly cheaper (10-20%) but it takes 3-5 WEEKS to get to Alaska (Dog sleds and all).
My point is that he might save 30, 40 or even 50 by buying a used unit off the EE, but by the time you tack shipping and everything on to it, he probably isn't saving much cash.