I was scared to trade or sell orchids for a long time. The only person that I knew who sold orchids did so out of her van. She went to shows and Farmer's Markets but never did mail orders.
One of my issues was getting boxes. Then I found the USPS shopping website. They offer lots of free stuff to help with shipping.
It makes sense, they may lose some money by giving stuff away, they make it back in efficient package handling using standard size boxes.
I have a stock of 3 or 4 sizes but my favorite is the shoe box. Almost all the plants I want to mail fit in the 14"x8"x5" size and quite often the total is under a pound. The top of plants takes space but is light. Crumpled newspaper keeps the plant from bouncing around.
If you have been putting off trading, explore the USPS website. Not only can you get free boxes, you can print your own postage. Then you can take it to the "Prepaid Drop off" in the post office without waiting in line.