Ballpark cost on a moose mount will be $1200-1500. You are right - they need lots of room. Basically think size of a longhorn steer.
I didn't do detachable antlers and didn't have any doorway issues. But would probably help in setup process. Took 3 of us to put mine on the wall (kinda high on the wall) - I remember thinking if I didn't hit the bolt in the wall the first time as we lifted it we might be in trouble.
Should go without saying, but find a stud and put your anchor in deep.