I to am interested in an m4 and ive done a lot of research on them. Im definatly leaning towards the bushmaster m4a3 (a3 means removable carry handle handle to accomadte optics more easily). You can probably find one new for around 950 if you look around. I would not go with a colt they are over priced and come with 1:7 twists, which unless you wanna shoot heavy bullets is too fast. The bushmaster has a 1:9 twist which is sort of a compromise. If you plan on shooting yotes with it id go with a 1:9 twist.