I recently fought this exact decision, and "overpaid" for a BRP manufactured German MG-42.
They retailed originally at a stiff $4,000 - I made my purchase on an auction at $4,600.
I did the same with the Polish PKM I acquired; paid $8,600 when they originally cost $5,895. The more rare Russian ones are selling for 2x what they cost.
Whether this is "overpaying", as with most rare, out of production things, is debatable.
Many would argue that paying anything over $70 for an SKS is overpaying, but I have one in my cabinet that I paid $270 for, and another (Russian) that I am considering at an even higher price point. The same holds true for ALL surplus arms which have gone up in value, including our very own M1 Garands, 1903's, and M1 Carbines.
If a firearm is no longer in production, or there is no longer a supply, it becomes a sellers market.
This is especially true if you only find ONE up for sale, and then, only rarely.
The seller is in the advantageous position of naming a price. It is up to the buyer to decide if he's willing to pay it. If there are not many potential buyers, it is up to the seller to decide how badly he wants to sell it. The buyer can make a lower offer but the seller has the final decision on whether to accept it, or to hold out to find a "better" buyer.
Look at it this way; when a firearm was widely available for sale, there was a supply of "X" - be that 250 units, 1,000 units, or 3,000,000 units.
Once a firearm is no longer available for general purchase, NOW the supply is how many people are selling them at any given time. The sellers have to compete against each other for buyers. If there is a limited pool of buyers, the sellers are at a further disadvantage. The most desperate seller "wins" the early sale, but loses potential value. As sellers drop off, and circulation settles in on long term owners, there are fewer sellers, less competition, and prices gradually rise.
If you only find ONE for sale, you're in a different market entirely.
Now you are 100% at the mercy of the seller, and you are competing with any other buyers. This drives the price REMARKABLY higher, and it happens very FAST.
This is how I am qualifying what guns to purchase for the "investment grade" part of my collection. You need to buy in when they are in ready supply, or before they reach the point of "single seller" market.