Get large lawn and leaf trash bags the thick ones. Put two tires in them with some layers of thick cardboard between them to protect the wheels, face the wheels together. Wrap the heck out of the whole thing with duck tape get all the loose ends so nothing can snag. I use a whole roll of cheap tape to ship a set of four.
Ship using Fed Ex Ground and drop them off to a distribution point (by air port normally). Should be about 30-60 any place in the cont. US.