For shipping containers, go down to your local Discount Tire place and ask about boxes or just look in their dumpster. They sell a lot of rims.
For the 16X8 GTA rims, I would try to use 17X9 boxes. Cut extra pieces of flat cardboard from other boxes to stack around & under/over the rims in the box for protection and tape the box like a bunch of gorillas are going to play with it. Figure $18-$25 shipping on each box.
HTH