I'd recommend the Romanian SAR-1. I bought two and am happy with them. They aren't finely made and finished rifles. But they work and are fun to shoot. AIM Surplus currently has them for about $300 each ($10 less if you buy several). Others probably sell for comparable prices. What I like about the SAR-1 is that it has a pre-ban "look and feel" (pistol grip stock, high-cap magazines, etc.). Be warned, however, that some have been known to have crooked front sight posts and most have mis-matched wood.
If you want to pay more, I think there are some nicer AKs around. The Bulgarian SSR99s sounded great, but I don't think they were available for long. AIM has some Russian AKs that could be good (I haven't heard anything about them yet). In general, milled receivers are considered better. Some of the thumbhole AKs are probably better quality than the SAR-1s and could legally be converted to pistol grip configuration if you install U.S. trigger parts, etc.
On the other end of the price scale, there are sub-$200 AKs that are limited to thinner 10-round magazines and thumbhole stocks. I understand some are of pretty good quality (Hungarian SA2000 (?)).
But I still think the SAR-1 hits the "sweet spot" for me. I don't think of ANY AK as a "fine rifle," so I can't get excited about paying $600-$800 for one. I'd rather get an AR or an FAL for that kind of money. But I enjoy shooting my SAR-1s. In fact, I just installed a Bulgarian-style black plastic stockset on one. And I've got a Kobra red-dot sight on order that should snap right onto the SAR-1s siderail mount. Come to think of it...I'm getting close to the $600 range with these add-ons! Oh well.
Regarding the caliber, I recommend the 7.62x39 (standard AK) caliber. There are rifles available in .22 calibers (.223 and a Russian version), but I don't see the point. These aren't long range, highly accurate rifles. I like the cheap, easy to find 7.62. It does probably kick a little more, but it is also adequate for deer and other medium game if you are so inclined. Good luck.
Doug
[This message has been edited by DougB (edited May 06, 2000).]