Your best bet would be a used Ruger Mini-14, I picked mine up for $325 and it's in perfect shape. A lot of people think this little rifle is suitable for use only as a boat anchor, but mine has been 100% reliable and is accurate enough for its intended purposes. No, it's not a tackdriver but if you want target-grade accuracy you'll be paying a lot more $$ for a rifle that will probably not be as reliable. Magazines are still fairly easy to come by, and since the gun is still in production, parts are no problem if you need them (you probably won't). Bottom line--don't knock the Mini-14 'til you've tried one. There really isn't anything to compare with it in this price range. Let us know what you end up buying--
Sic semper tyrannis
freedomlover