A couple of things, if the monorail line really only cost a million dollars a mile Disney would be working triple time right now to connect every part of their property. They currently have a little more than 40 miles of track so if they could double it for only 40 million, believe me they'd do it. Everest cost just north of 100 million to build.
As for the monorails, they run at almost peak efficiency. The monthly run rates average about 99.8% fact is they're far more reliable and cost less per mile to operate than the buses. With that said however, buses are more easily replaced and people are far more easily evacuated from buses. Not so with the monorails.
So, the major obstacles to getting additional monorail lines built is the cost per mile figure more like 5-10 million per mile, the cost to construct new monorail stations and the cost of new cars.