I met Randy for over 20 years ago and bought a number of pistols from him, and sold a few to him. He originally dealt only in high quality autopistols and was a real expert. His prices were not cheap but not bad either.
He has branched out into other weapons over the past 10 years and I haven’t been in touch with him during this time. During the time I knew him well, he had zero interest in cartridges.
Most of the guns that he had for sale were on consignment. I suspect he has had some ammo put on consignment along with guns and it is easy to list it on his website. The original owner likely told Randy what he wanted for the cartridge, and Randy added his markup and there is the result.
I have run across a number of gun collectors who want ammunition, mostly boxes as accessories to their guns, and the prices they are willing to pay have about one more zero on the end (ahead of the decimal) than what I would consider a marginally outrageous price.
The truth is cartridges are like any other collectible. The a person is willing to pay depends on how bad they want it.
Almost 40 years ago, person once told me he had located a full 16 round box of German, early WWII, Polte aluminum case 9mm P08 cartridges, and asked me what they were worth. Clearly it was a joke, but I decided to play along. I told him the first two were worth $1000 and told him the names of those who would pay that. The next three were in the $500-$600 range and provided the names. Then there were four or five in the $100-$200 range and the rest would sell for $50-$75. I told him that I was interested in buying the last one along with the box for $50 each. At that time this was probably a valid assessment of the value of this mythical cartridge.
The price depends on what a person (or in an auction, two people) are willing to pay. A few years ago, I’m told a 9mm Borchardt sold in Germany at auction for about $2500. At about the same time one sold in a private sale in Europe for $1000. More recently one sold in US for $600. What is a fair price? All three were fair, it just depends on what the seller is willing to take and what the buyer is willing to pay.
We can discuss this for ever, but for me, the bottom line that a person can ask whatever price they want for an item. It is their property and their decision on what it is worth for them. It is the buyers decision on how bad he wants it.