I read somewhere that the cost of building elevated train systems has shot up several hundred percent in the last couple of decades, outpacing inflation by a large margin. I don't think a major elevated train system has been installed or expanded in the US since the 80's. There are elevated portions of some new light rail, but they are relatively short [[Seattle's system at SeaTac.)

Disney wanted to build out their monorail system to service their new hotels, but the cost per mile went from $1 million in the early 80's to $15 million in the 90's, and it's even more now.