From what I've seen, the 16" barreled Saigas (or the 21" ones that have been chopped down to 18 or so) tend to be about as accurate as a standard model M1A, though not quite on the level of some of the more precision oriented M1A models like Loaded, NM, Super Match, etc... as was said, the 16" barrel does lose some velocity to the M1A's 22" tube, and has a much more apparent muzzle blast and flash. The 21" barreled Saigas do appear to suffer from barrel whip and tend to be less accurate (but still good enough to get you hits on man-sized targets out to 500 yards or so).
One nice thing about the Saiga compared to the M1A is that the Saiga has a chrome-lined barrel, while Springfield does not offer them anymore on any of their rifles. To get that option on an M-14 platform, you have to go with a mfg. with a higher price point than Springfield.
The one weak point on Saigas used to be the lack of an available standard capacity mag, but now there are some 20 rounders on the market for a fairly decent price. Of course that has caused the demand and prices to go up (you used to be able to get one for under $400, but now they routinely go for over $600). $500 is definitely a good deal for one.