BI4AVZ I think it would be better if someone else took on the task.
I have too many cards here, and it's not really suitable for you to transfer them here either.
The main method currently used is to send goods via discounted tickets and land transport.
I estimate that a 1kg "card" would cost around 40 yuan.
However, you can buy some cheaper tickets with the same design, or use postcards with advertising and stamps. Since the QSL card will be discarded after being placed in the recipient's mailbox, the envelope itself is not that important.