Dorkfish,
All of the research that I have done points to the Saiga as being the best bang for the buck. I have one that I converted and I don't think I have much more than $500 into it. I really like that rifle.
As has been suggested, if you buy the rifle and then convert it yourself, it will be about $500, but if you are buying one POST conversion, its going to cost you a lot more. My personal theory on that is that it can take a couple hours or more to do the conversion, so you're getting stuck with the bill from havign a gunsmith undo some screws and redo the trigger guard.
I know that some of the conversions out there look pretty complicated, but they really aren't that hard. I remember when I first was starting it out, and alot of people said "If I can do it, You can do it" and I thought "Yea, right." Actually, they were right. Keep in mind, these guns are worked on by guys in caves with primative hand tools. If they can do it, you can do it.
You can probably do it with just a screwdriver and a cordless drill, but I would recomend using a dremel tool for some of the stuff. If you don't have a dremel tool and a cordless drill, do yourself a favor, and buy them. No, seriously, they are great tools and with them you can do a lot of different jobs, gun related or not.
Heres something to help you get started:
http://forum.saiga-12.com/
Thats one of the main Saiga forums, and even though it says Saiga 12, they cover the rifles too. There should be a pretty good video tutorial on there that will walk you through it.
You really owe it to yourself to do some research before you buy.
as far as the exposed gas tube goes, I personaly prefer the full length saiga handguard. It allows you to hold the gun wherever you want, not just one location.
I run my Saiga with regular AK mags - you just have to add a bullet guide (its pretty simple) and shave off some of the mag release (also pretty simple)
Hope this helps.
Chris "the Kayak-Man" Johnson