I'm over here (old Dice Clay joke)!
I've never personally handled (read as fondled) any of the A model rifles. All of mine are the traditional B models. So I can't honestly say how they run.......but they're still Armalites. That being said. I don't think that I've ever seen any of the lowers available separately. Hell, the B lowers were hard enough to find up until about 8 months ago (or so). I'm with Tom on this one. Go for a complete rifle, and modify accordingly. There are some pretty good deals out there (the 12 to 13 range) that I see on these rifles periodically.