I have shipped lifesize gemmys all the way to New Zealand , without a scratch.
shipping cost is actually reasonable.. so don't let that deter you. Besides, the buyer is paying for that. Let him or her decide if, the cost is reasonable.
if you have its original box.. that is ALWAYS the best.
if you don't.. go to walmart and purchase TWO "large shipping boxes" they are 18 x 18 x 24. They are found in the same section as shipping tape/packing material.
the first one forms the bottom of the box. the second, you slide ontop to form the top. total size of box will be 18 x18 x 38
the prop will fit in the box, diagonally.
good luck!!