Centerfire systems has AMD's for $439 right now.
If you want total control of what features you want on your rifle and are open to some work, I might also suggest looking into the Saiga's. They are very affordable in their imported form (Around $380'ish) and really are not rocket science to convert back to a standard AK trigger/grip system. You will of course have to devote some cash into the conversion, so it would probably come out to more than the AMD in the long run, though you'd have the rifle just as you want it. There are a bajillion aftermarket parts that will fit it and tune it to pretty much any configuration you might want, including side folders. There are the Polish and Romanian Side Folders, the ACE Style side folding stocks, AR stock adapters that you can add a side folding hinge to, and many other side folding stocks (such as This one).
There is also this neat stock I just found out about yesterday. It's very HK'ish, sounds like it provides what you are looking for, and doesn't break the bank at all. I've heard it's pretty dang solid and locks up tight. You can also get one that mounts using an AR adapter, and if you get the proper adapter the stock won't sit at that funny angle and will flow with the receiver. It doesn't interfere with the firing of the weapon in either case, aside from if you have large hands and are using the AK specific model - but it'll probably make the grip a bit uncomfortable in that case, though the weapon would still fire.
Hope this helps!
