It's a pretty big old marquee to bung on email you know

I understand that they are also non-retrievable, right?

So... 20k and you can't work as a team to delegate supplying camps to avoid over purchasing such things, nor can you send one to a guild mate/friend who needs it but is a far Far FAR horse ride from their nearest siege merchant, nor can someone pick up their expensive camp after it has served its purpose.