No country which manufactured the SKS gave it the nomenclature of M21. The only country which applied an "M" number which I can think of offhand was Yugoslavia, who designated theirs M59, and M59/66 for rifles which had the 22mm grenade launcher fitting. Yugo SKS rifles can go from $150 - $500, with the latter price being for an unfired, unissued rifle. SKS rifles in general can go from $100 - $1300, depending on the exact model and country of manufacture (Vietnamese and North Korean rifles have the highest value, being the most rare). You can send photos of the rifle and markings to my email (listed on my profile page), and we can determine the exact model and value from there, if you wish.
The M21 and Enhanced Battle Rifle are two different variations of the M14 rifle, both of which are very much real.
50-500 USD depending on specifics
$100 to over $1000, depending on the specifics.
Around $300- depending on condition and originality
Priceless, since a true SKS assault rifle would be a prototype only most likely. The SKS fires semi-automatically and does not have provision for full auto fire. If you have a normal run of the mill Chinese SKS it is worth 100-400 or so depenidng on condition, box, accessories, etc..
Many makers have had a M21. You might be referring to a variant of the M14 used for sniping @ Vietnam era.
No. PA does not require gun registration- and the SKS is not an assault rifle- it is a semi auto rifle with a fixed magazine.
SKS
One can purchase an SKS rifle from a variety of locations. These include a good hunting store, a rifle store, and some of the larger supermarkets such as Walmart.
Value of Rifle by Norinco SKS 7.62x39 with and without wood stock?
romanian serial number 1841899n sks rifle what year is this rifle
18, just like any other rifle.