I'm looking into building an ar-15. I had planned in other guns first, but my wife seems okay with the idea of slow building and buying. I am seeing all kinds of lowers for $40-$70 stripped. Are these cheap cheap options a good place to start? Are there some with LPK already installed in that price range? I have a friend that would help with the tools etc. To build. Final question if I start with a normal 5.56 build can I throw a 22lr upper on it and switch back and forth?