No published sn data.
They can go anywhere from $200 to well over $1200, depending on condition and country of manufacture.
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.
Year of Manufacture is stamped behind the serial # on the left side of the receiver.
First off, you didn't specify which army, nor did you specify the country of manufacture - the SKS was manufactured in the former Soviet Union, Romania, East Germany, North Korea, Vietnam, the Peoples' Republic of China, the former Yugoslavia, and Albania. A lot more information would be needed in order to determine this. Bear in mind that not all SKS rifles manufactured saw military service - many of the M59/66 rifles were never issued, and China continues to manufacture the SKS for the commercial civilian market.
No published sn data. 50-300 USD or so depending on specifics
people who live in Hungary are called Hungarians
SKS Microfinance was created in 1998.
Depends on country of manufacture and condition. I am not aware of any publicly available serial number lists for any of the SKS manufacturers, so that is not a helpful bit of info. Russian SKS carbines are the most valuable at this point, with some in excellent condition reaching $400. They are followed by Chinese and Yugoslavian. A beatup Yugo with a rusted gas valve will fetch $100 on a good day.
The D and M models accept AK47 magazines whereas the standard sks has an integral magazine.
The only SKS carbines currently which require registration are the Chinese-made SKS-M and SKS-D models. Those could not be imported into the state after 1989, and had to be registered by 2000.
All of the fixed ten round mags are cross compatible, but cannot be used in the SKS-M or SKS-D, both of which use a detachable AK magazine.