Values ascribed to firearms are very subjective and market based. They are assigned according to rarity, historical-political interest, appearance and completeness.
A complete all matching K98k with history (verifiable vet bring back with documents) is worth close to $1,000. A Soviet capture mix master is worth $300. Put a swastika on any item, and suddenly it has significant value.
For years in Canada, surplus Lee Enfield rifles were bought for next to nothing, cut up and sporterized. They had no value. Slowly, as the last generation to carry that rifle in war started to age and die, younger collectors wanted to obtain a tangible piece of their forefather's history. Complete matching original examples commanded higher value over the mismatched and chopped examples.
M1 rifles could be bought for reasonable coin at one time. There was no great demand for them, couldn't be sporterized, were heavy, clunky and just not an '03 Springfield. Once again, as interest gained momentum among collectors for the arms and equipment of their father's generation, values continued to rise.
We now see the emphasis on restoration and preservation, not abomination. A cut up No.1 MkIII may fetch $60. Find the same unmolested rifle with pre-1916 features (volley sights, mag cut off, stacking swivel, original stock) and Canadian acceptance stamps, and you will need another $500.
Twenty years ago, publications providing detailed study on specific martial arms, history, production, variants, prototypes, ancillary equipment, etc. were few and far between. They were often filled with poor quality photographs and erroneous information. Now even novice collectors can find a wealth of information both in print and on the Internet.
Collecting imposes it's own standards of monetary value. Whether its vintage cars, stamps, coins, books, manuscripts, or any other memorabilia. You have to appreciate that forums like this appeal to firearms enthusiasts with diverse interests. Some are plinkers, some are collectors, some both.
Interest in Soviet arms and equipment is still relatively new. Before the arrival of these SKS carbines, your typical SKS-45 commanded prices in the +$400 area. Mosin Nagant rifles, Tokarev and Nagant pistols, SVT-40 rifles, were few in number, usually Finnish capture sourced items. While still relatively cheap, that can change in an instant.
Look south of the border to the USA. The SVT-40 and SKS are banned from further import. Their values have increased greatly. No, you can't retire by selling one SKS. But when I see a Chinese Type 56 SKS, which could be purchased from MARSTAR two years ago for $139, sell at auction for $350 or more? The average firearms enthusiast is not some independently wealthy fop. A couple of hundred dollars can be the difference between affordable or not.
kwhunter, you know that an early '70's limited production muscle car in pristine original condition has greater value then one that's been restored or a standard model humped up to look like the rare original.
Same applies to firearms. I hope my explanation is of help.