Depends what the stuff is worth to the purchaser, really. He's got to pay to store the stuff and it does take time to do inventory, power stuff on to see if it works, etc. He quoted me a 6' GPIB cable for $10 — which could be viewed as expensive for such a basic piece of retrotech, yes, but considering new ones cost $40 or more, not unreasonable.
I find that the biggest expense with the stuff I buy, from any seller, is shipping charges, and no one can do anything about that when the stuff is 2000 miles away or more, and weighs a ton to boot.