Value of ANY gun is based on exact make, model, and condition. A well worn Yugo SKS may be $150, while a pristine Russian SKS is $500. An average Chinese SKS is around $250-$275.
Russian
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Dependent on condition, anywhere from $300 - $500.
$300-$500, depending on condition and originality.
Very similar, minor differences,
Importer name
they are about $100
This is purely opinion on my part, but the SKS was created in Russia, and made there for a number of years before the Chinese began manufacture. The Russian SKS tends to have better quality machining than the Chinese. Both are good, but the Russian is the original, and the better built rifle. Examine one of each side-by-side, and see what you think.
20-45 USD
Markings.
The RUSSIAN SKS may be date marked on top of the receiver cover (properly called the rear housing) , along with the symbol of the arsenal that made it.