I collect pocket watches and guns and have cons #'s of each. A rule of thumb is 50% of one item, so a $2k gun with its sibling would be $5k.
This only holds true if someone wants them. The guns are SAA Colts, 3rd gen nickel, factory ivories, 45 in 4 3/4. A desirable combination to have in pairs... although first gen would put a lot more bling into it. The SAA's were often ordered in cons pairs, meaning there was and is a demand for them. If these were rem 1100 shotguns, the premium would be near zero. So there is a "how neat would it be to have a cons pair" factor working here.
The other consideration is the relative price of one gun. The premium on a $300 gun would be $150, alot easier to swallow than a $1k premium on the model 66 3".
I would be willing to bet if someone posted a cons # pair of 1947 K22 one line address, large ejector knob in excellent condition for $2k, they wouldn't last long.
Charlie