Length: approximately 40 inches (most examples)
Barrel Length: approximately 20 inches (most examples)
The SKS was adopted by the Soviet Union in 1949, but was quickly phased out in favor of the AK-47. Many other countries adopted the SKS and the Chinese particularly favored the design. Most examples feature a fixed box 10 round magazine. The original fixed magazines are typically very reliable. Aftermarket 30 and 40 round magazines can be fixed in place of the original, but I have never used one that fed properly for all 30 rounds. Some Chinese models have been made to accept AK-47 magazines. Most models were fitted with an attached blade or spike bayonet that could be extended and fastened into place.
Yugoslavian models are usually the heaviest, but have more standard features than most models. Chrome is not native to Yugoslavia, so the barrels were not chrome lined, leaving the majority of examples dark. The above picture is a Yugoslavian M59-66A1. Models with the grenade launching fixture as pictured have a gas cut off switch that allows the rifle to be used like a bolt action rifle. An outpouring of these rifles came to the United States in the 1990s and 2000s, some unfired, and most were well preserved. These have largely dried up.
Pictured is a Russian SKS that was refurbished in Ukraine. These examples feature blued metal and the wood has been shellacked similar to the way that the Russian capture K-98K rifles were refinshed. Russian examples, even refinished will command a premium.
Prices vary wildly in the United States, unfortunately often depending on the current political climate. About $300-450 currently is the norm, depending on the make, model, and condition of the rifle. Long gone are the days of the late 1980s and early 1990s when a new in the box Chinese SKS would cost around $90.
The following volume on the SKS carbine provides an excellent overview of the rifle over time: