Last week I shipped a small 5x5 to WV from Colorado.
I made the shipping container for about $15 in materials.
Used a strap to wrap and secure antlers and screwed it to the frame.
Shipping via UPS was about $260
It may not be your preferred method but when I was doing taxidermy we would cut the antlers off with a fine saw blade as high as we could on the bases. Then a hole would be drilled into the base and into the bottom of the antler. A wooden dowel would then be inserted into the bottoms of the antlers to re attach after shipping. This saves you a ton but creates a little more work.