I think the SKS is one of those easy-to-find, tried-and-true designs that are drawing a variety of prices right now.
As for the things about them that don't change with price are that they are rock solid (speaking for the Yugos from experience, more the better if you can find the early ones known as M59's; made without a grenade launcher sticking off the muzzle). I find them very quick and easy to reload as well in the original configuration. If you're looking for maximum firepower get a Norinco and go hog wild with AK mags. There's not a lot of differentiation where accuracy is concerned from make to make, as the SKS just isn't made to be very accurate at or beyond 100yds (not that there aren't exceptions, good examples that shoot better, etc., I'm just giving the broad strokes on the weapon as a whole). Reliably cycles the cheap ammo, which is great because there's no point in buying the good stuff (see accuracy comments above).
Now, as to price. I can see why some pay the upper end (I'd say $300+ right now) for a Russian, Yugo M59, or maybe an unfired Norinco. Don't know about the Romanians, Poles, other rare makes. The ubiquitous Yugo M59/66 with the grenade launcher is a workhorse and shouldn't be in the 'high' range.
IMHO no need to convert to magazines (stripper clips are great) so no need to worry about all that. There are some cool Yugos that have been used in combat in the 90's and have stock carvings, checkpoint markings, etc. in some nice wood that make a good project for an original condition milsurp rifle (mine belonged to a guy named 'Dano').