Go to local shop, and get a box. Or you can build one yourself.
I typically tape the ski's together. I will grab an old pair of socks to slip over both ends of the ski's, and bubblewrap in one layer. Stuff newspaper in both ends of the box to keep the ends of the ski's from being banged around or sliding around in the box. USE A FUCKTON of packing tape. Not duct tape.
USPS is the best as far as price goes. Get delivery confirmation.