There are length restrictions using USPS (Equivalent to Australia Post) which generally cancels out the opportunity of sending skis (There have been cases where a USPS worker has just turned a blind eye or forgotten, so they have got through though)..
This is why international couriers are used e.g. Fedex, DHL, UPS etc - and they are far more expensive. You could expect to pay anywhere between US$100-200 to ship skis using any of these couriers (Depending on who the sender is, as businesses often get a volume/industry discount)
Theoretically, I guess you could use a large sea freight company like NYKLine but with any of these large freight companies I think you generally purchase a portion of a shipping container, which most certainly wouldn't work out financially..
I think the best bet is to use a courier, it's expensive, but it's quick and reliable.
Which skis are you looking to get and for how much? I'm in Aus and there should be some good deals floating around..