As Denfoote said, most Makarovs use 8-round magazines. There are both military and commercial versions, from Russia, Bulgaria, East Germany, China, and maybe other places I don't know about. There are some Russian commercial Maks that use double-stack high capacity magazines. I don't think they are especially rare, although they aren't nearly as common as the standard 8-round versions. Up until six or eight months ago, dealer cost on Bulgarian Maks in excellent (near new) condition was about $110. East Germans cost maybe $50-$60 more (and probably not in quite as nice condition). The supply seems to have dried up, so I think prices are roughly $20-$30 more now. Of course, you have to add shipping and dealer markup to this. I would guess that Maks are now starting at around $170 or so retail.
Just to clarify one more point, the 9mm Makarov cartridge is not the same, or as powerful, or interchangeable with, the 9mm Luger (the cartridge most people think of when they hear 9mm).
Regarding the model to choose, I have only two Maks, both Bulgarian military models. I'm very happy with them. The East Germans seem to be the most sought after and have a reputation for having the best workmanship (I think the difference are very slight, however). I don't think you'll go far wrong with any Mak you find - I'd probably get the one you find a deal on (maybe at a pawn shop).
You can learn a lot more on
www.makarov.com.
Doug