They're one of the best systems out there right now.
I shoot USPSA with one, and indeed they are dominant.
Since they aren't imported any more, prices have began to climb. Lots of people remember when CDNN bought the reamining EAA stock of them and was blowing them out for super dirt cheap, thus they are unwilling to pay the higher prices as it's been etched into their minds that Saiga 12's should sell for $229, or whatever artificially low price CDNN had them for.
The issue with them is magazines.
There just aren't enough to go around, and the prices have gotten quite testy. The 8 rounders were hens teeth to begin with, so needless to say the prices on them are in the stratosphere on ebay. Even the 5 rounders are $60-$75 each, when you can find them.
There are a few sellers overseas who offer S12 magazines, but it seems that the Saiga plant doesn't produce them in large numbers and it's usually a few month wait to lay hands on one (not including transit times)
The conversion process from sporter to PG isn't that hard for the handy types who can run a dremel and a drill, but it is a bit labor intensive and isn't for everyone.
You are seeing converted guns selling for $600+ right now, with sporters in the $400 range.
If you find one below $400, buy it's a good deal for this market.
If you luck into a dealer who has one as old stock and is selling it for his typical $100 markup over what he paid CDNN, it's dumb luck and you should be sprinting for your checkbook.
As of right now, there is no central wholesale source for S12's, thus you are at the mercy of the secondary market.
There is an outfit called RAA that is supposed to be reimporting them, but you can be for darn sure that they won't be at CDNN 'Buyout Stock' blowout prices, so the premium you pay today isn't that great over what they will assuredly charge should ATF ever clear them to be reimported again.